Flash detection

ABSTRACT

The present disclosure provides a method including memorizing a sequence of high-resolution images of a scene in a buffer, obtaining radiation emission readings from one or more photo detectors, detecting a suspected flash event based on processing the radiation emission readings from the one or more photo detectors. The method may further include that the detecting occurs at a first instant, retrieving from the buffer high-resolution images of the scene including at least one image that was captured prior to said first instant, and processing the high-resolution images of the scene to determine a geolocation of the suspected flash event.

This is a Continuation of U.S. application Ser. No. 14/625,210 filedFeb. 18, 2015, which claims the benefit of priority of IsraelApplication No. 231111 filed Feb. 24, 2014. The disclosure of the priorapplications are hereby incorporated by reference herein in theirentirety.

FIELD OF THE INVENTION

The present invention is in the field of flash detection.

ACRONYMS

SWIR Short Wave infra Red (1-2.5 μm)

Extended SWIR 1.8-2.5 μm

Lattice matched SWIR 1-1.7 μm

MWIR Mid Wave Infra Red (3-5 μm)

LWIR Long Wave Infra Red (8-12 μm)

Near Infra Red (0.7-1.0 μm)

Vis Visible light (0.4-0.7 μm)

SBUV Solar Blind UV (0.24-0.28 μm)

Pd Probability of Detection

FAR False Alarm Rate

SCR Signal to Clutter Ratio

SNR Signal to Noise Ratio

FOV Field Of View

IFOV Instantaneous Field Of View

BACKGROUND

U.S. Pat. No. 8,304,729 to Snider proposes methods, systems andapparatuses that detect, classify and locate flash events. In someimplementations, some of the methods detect a flash event, trigger animaging system in response to detecting the flash event to capture animage of an area that includes the flash event, and determines alocation of the flash event.

U.S. Pat. No. 8,421,015 to Scott et al., discloses an event detectionand classification system which uses a type of optical sensingcomponent, a Position Sensing Detector Focal Plane Array (PSD-FPA). ThePSD-FPA provides for high-speed operation that allows for accuratesensing of fast artifacts that are unique to weapons fire and enablesprecise location of optical phenomenon. The system detects andclassifies events, particularly weapons fire, and rejects false alarms.An optical lens sub-system focuses light onto a PSD-FPA, which sensesthe photons and generates electrical signals associated with individualelements of the PSD-FPA. These signals are processed to identify andclassify weapons-related or other events. Background subtraction,variable gain, time-intensity and time-location correlation, digitalfiltering, Fourier analysis, and wavelet analysis are all used tosuccessfully classify the events while rejecting false alarms.

U.S. Pat. No. 7,619,754 to Riel et al. discloses curved sensor arrayconfigurations and methods of processing the data gathered by thesensors. A 2 dimensional embodiment comprises singular ring of sensorsthat can monitor sources in a 2 dimensional plane. A sensor directlyfacing a target produces a maximum response. As the angle of a sensorrelative to the target increases, the response decreases. Fitting thesensor response amplitudes to a 2D Gaussian curve and calculating, thepeak of the curve allows a very accurate calculation of the angulardirection of the target. A 3D embodiment comprises sensors distributedover the surface of a sphere in order to monitor multiple targets in anyspatial orientation. Again, the sensor amplitude data is fitted to a 3Dcurve or surface such as a Gaussian surface. The present invention canresolve more than one target using deconvoluting techniques.

U.S. Pat. No. 3,936,822 to Hirschberg discloses a round detecting methodand apparatus for automatically detecting the firing of weapons, such assmall arms, or the like. Radiant and acoustic energy produced uponoccurrence of the firing of the weapon and emanating from the muzzlethereof are detected at known, substantially fixed, distances therefrom.Directionally sensitive radiant and acoustic energy transducer meansdirected toward the muzzle to receive the radiation and acousticpressure waves therefrom may be located adjacent each other forconvenience. In any case, the distances from the transducers to themuzzle, and the different propagation velocities of the radiant andacoustic waves are known. The detected radiant (e.g. infrared) andacoustic signals are used to generate pulses, with the infraredinitiated pulse being delayed and/or extended so as to at leastpartially coincide with the acoustic initiated pulse; the extension ordelay time being made substantially equal to the difference in transittimes of the radiant and acoustic signals in traveling between theweapon muzzle and the transducers. The simultaneous occurrence of thegenerated pulses is detected to provide an indication of the firing ofthe weapon. With this arrangement extraneously occurring radiant andacoustic signals detected by the transducers will not function toproduce an output from the apparatus unless the sequence is correct andthe timing thereof fortuitously matches the above-mentioned differencein signal transit times. If desired, the round detection information maybe combined with target miss-distance information for further processingand/or recording.

U.S. Pat. No. 5,686,889 to Hillis described how firing of small armsresults in a muzzle flash that produces a distinctive signatureconducive to automated or machine-aided detection with an IR (infrared)imager. The muzzle flash is intense and abrupt in the 3 to 5 μm band. Asniper detection system operating in the 3 to 5 μm region must deal withthe potential problem of false alarms from solar clutter. Hillisproposes to reduce the false alarm rate of an IR based muzzle flash orbullet tracking system (during day time) by adding a visible light(standard video) camera. The standard video camera helps detect (andthen discount) potential sources of false alarm caused by solar clutter.If a flash is detected in both the IR and the visible spectrum at thesame time, then the flash is most probably the result of solar clutterfrom a moving object. If a flash is detected only in the IR, then it ismost probably a true weapon firing event.

U.S. Patent Application Publication No. 2011/0170798 to Tidhar disclosesa device and a method for use in detection of a muzzle flash event. Thedevice can include a Photo Detector Array (PDA), sensitive in at least aportion of the NIR and SWIR spectrum, and a filter of electromagneticradiation selectively passing in this portion a spectral range of lowatmospheric transmission, the PDA has an integration time shorter than aduration of the muzzle flash event.

SUMMARY

In accordance with an aspect of the presently disclosed subject matter,there is provided a method comprising:

memorizing a sequence of high-resolution images of a scene in a buffer;

obtaining radiation emission readings from one or more photo detectors;

-   -   detecting a suspected flash event based on processing the        radiation emission readings from the one or more photo        detectors, wherein said detecting occurs at a first instant; and        retrieving from the buffer high-resolution images of the scene        including at least one image that was captured prior to the        first instant;    -   processing the high-resolution images of the scene to determine        a geolocation of the suspected flash event.

In addition to the above features, the method according to this aspectof the presently disclosed subject matter can optionally comprise one ormore of features listed below as different embodiments, in any desiredcombination or permutation.

In accordance with an embodiment of the presently disclosed subjectmatter, the method further comprises operating a high-resolution camerawhich captures the high-resolution images independently from thephotodetectors, and from a detection of a suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, the method further comprises capturing the high-resolutionimages continuously regardless of a detection of a suspected flashevent.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein at least one of the high-resolution images retrievedfrom the buffer precedes the appearance of the suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein a sampling rate of the photo detectors is higher thanthe frame rate of the high-resolution camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein a sampling rate of the photo detectors is at least 5times higher than the frame rate of the high-resolution camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photo detectors operate at a cut-off wavelengthwhich is higher than the cut-off wavelength of the high-resolutioncamera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the I-FOV of the high-resolution camera is at least 10times smaller in at least one axis than the FOV of at least one of theone photo detector.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photo detectors operates with a cut-off wavelengthwithin the extended SWIR range, which is between 1.8 μm to 2.5 μm, abovethe Lattice Matched SWIR cuttof of 1.7 μm

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera operates with a cut-offwavelength within the SWIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is adapted to captureradiation mainly within an atmospheric absorption band.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera operates with a cut-offwavelength within the NIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is a bolometric camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises spectral domain processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises intra-flash time-domain processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises total energy processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the spectral domain processing comprises processingradiation emission readings captured over a majority of a duration ofthe suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the intra-flash time-domain processing comprisesprocessing radiation emission readings captured over a majority of aduration of the suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, further comprising determining based on a processing of theradiation emission readings from the one or more photo detectors, andbased on a processing of the selected images, whether the suspiciousflash event is an event of interest or not.

In accordance with an embodiment of the presently disclosed subjectmatter, further comprising determining based on a processing of theselected images whether the suspicious flash event is an event ofinterest or not.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing of the selected images comprises: spatialdomain processing and temporal-spatial processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein capturing the high-resolution images comprises operatingthe high-resolution camera with an inter-exposure interval that isshorter than the shortest possible pulse duration of a suspected flashevent.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein capturing the high-resolution images comprises operatingthe high-resolution camera at wavelength band which is different fromthe wavelength hand at which any one of the photo detectors operate, andwherein the determining whether the suspicious flash event is an eventof interest or not comprises cross wavelength band processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the obtaining radiation emission readings from one ormore photo detectors, comprises obtaining a plurality of radiationemission readings from the one or more photo detectors during a flashduration, and comparing attributes of the plurality of radiationemission readings to a library of flashes.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the radiation from at least two FOVs is superimposed toprovide a single high-resolution image, and wherein the geolocation isdetermined using information about a rough geolocation obtained from theone or more photo detectors which provided the radiation emissionreadings.

In accordance with an aspect of the presently disclosed subject matter,there is yet further provided a method comprising:

memorizing a sequence of high-resolution images of a scene in a buffet;

obtaining radiation emission readings from one or more photo detectors;

detecting a suspected flash event based on processing the radiationemission readings from the one or more photo detectors, wherein thedetecting occurs at a first instant; and

retrieving from the buffer high-resolution images of the scene includingat least one image that was captured prior to the first instant;

processing the high-resolution images of the scene to determine whetherthe suspected flash event is an event of interest or not.

In addition to she above features, the method according to this aspectof the presently disclosed subject matter can optionally comprise one ormore of features listed below as different embodiments, in any desiredcombination or permutation.

In accordance with an embodiment of the presently disclosed subjectmatter, the method further comprising operating a high-resolutioncamera-Which captures the high-resolution images independently front thephotodetectors, and from a detection of a suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, the method further comprises capturing the high-resolutionimages continuously, regardless of a detection of a suspected flashevent.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein at least one of the high-resolution images retrievedfrom the buffer precedes the appearance of the suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein a sampling rate of the photo detectors is higher thanthe frame rate of the high-resolution camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein a sampling rate of the photo detectors is at least 5times higher than the frame rate of the high-resolution camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photo detectors operate at a cut-off wavelengthwhich is higher than the cut-off wavelength of the high-resolutioncamera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein I-FOV of the high-resolution camera is at least 10 timessmaller in at least one axis than the FOV of at least one of the one ormore photodetectors.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photodetector operates with a cut-off wavelengthwithin the extended SWIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera operates with a cut-offwavelength within the SWIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is adapted to captureradiation mainly within an atmospheric absorption band.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera operates with a cut-offwavelength within the NIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is a bolometric camera.

In accordance with an embodiment of the present disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photodetectors comprises spectral domain processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises intra-flash time-domain processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises total energy processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the spectral domain processing comprises processingradiation emission readings captured over a majority of a duration ofthe suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the intra-flash time-domain processing comprisesprocessing radiation emission readings captured over a majority of aduration of the suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, further comprising determining based on a processing of theradiation emission readings from the one or more photo detectors, andbased on a processing of the selected images, a geolocation of the eventof interest.

In accordance with an embodiment of the presently disclosed subjectmatter, the method further comprises determining based on a processingof the selected images a geolocation of the event of interest.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing of the selected images comprises: spatialdomain processing and temporal-spatial processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein capturing the high-resolution images comprises operatingthe high-resolution camera with an inter-exposure interval that isshorter than the shortest possible pulse duration of a suspected flashevent.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein capturing the high-resolution images comprises operatingthe high-resolution camera at wavelength band which is different fromthe wavelength band at which any one of the photo detectors operate, andwherein determining whether the suspicious flash event is an event ofinterest or not comprises cross wavelength band processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the obtaining radiation emission readings from one ormore photo detectors, comprises obtaining a plurality of radiationemission readings front the one or more photo detectors during a flashduration, and comparing attributes of the plurality of radiationemission readings to a library of flashes.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the radiation from at least two FOVs is superimposed toprovide a single high-resolution image, and wherein the geolocation isdetermined using information about a rough geolocation obtained from theone or more photo detectors which provided the radiation emissionreadings.

In accordance with an aspect of the presently disclosed subject matter,there is yet further provided a system comprising:

a frame buffer capable of memorizing a sequence of high-resolutionimages of a scene;

one or more photodetectors capable of obtaining radiation omissionreadings from the scene;

a controller is configured to detect a suspected flash event based onprocessing the radiation emission readings from the one or more photodetectors wherein said detecting occurs at a first instant; and

wherein the controller is configured to retrieve from the bufferhigh-resolution images of the scene including at least one image thatwas captured prior to the first instant, and

wherein the controller is configured to process the high-resolutionimages of the scene to determine whether the suspected flash event is anevent of interest or not.

In addition to the above features, the system according to this aspectof the presently disclosed subject matter can optionally comprise one ormore of features listed below as different embodiments, in any desiredcombination or permutation.

In accordance with an embodiment of the presently disclosed subjectmatter, the system further comprises a high-resolution camera which isconfigured to capture the high-resolution images independently from thephotodetectors, and from a detection of a suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is configured to capture thehigh-resolution images continuously, regardless of a detection of asuspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein at least one of the high-resolution images retrievedfrom the buffer precedes the appearance of the suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein a sampling rate of the photo detectors is higher thanthe frame rate of the high-resolution camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein a sampling rate of the photo detectors is at least 5times higher than the frame rate of the high-resolution camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photo detectors operate at a cut-off wavelengthwhich is higher than the cut-off wavelength of the high-resolutioncamera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the I-FOV of the high-resolution camera is at least 10times smaller in at least one axis than the FOV of at least one of theone or more photodetectors.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photo detector operates with a cut-off wavelengthwithin the extended SWIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera operates with a cut-offwavelength within the SWIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is adapted to captureradiation mainly within an atmospheric absorption band.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera operates with a cut-offwavelength within the NIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises spectral domain processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises intra-flash time-domain processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises total energy processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the spectral domain processing comprises processingradiation emission readings captured over a majority of a duration ofthe suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the intra-flash time-domain processing comprisesprocessing radiation emission readings captured over a majority of aduration of the suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the controller is further configured to determine basedon a processing of the radiation emission readings from the one or morephoto detector, and based on a processing of the selected images, ageolocation of the event of interest.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the controller is further configured to determine basedon a processing of the selected images a geolocation of the event ofinterest.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing of the selected images comprises: spatialdomain processing and temporal-spatial processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is configured to have aninter-exposure interval that is shorter than the shortest possible pulseduration of a suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is configured to operate atwavelength hand which is different from the wavelength hand at which anyone of the photo detectors operate, and wherein determining whether thesuspicious flash event is an event of interest or not comprises crosswavelength band processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photodetectors are adapted to obtain a plurality ofradiation emission readings from the one or more photo detectors duringa flash duration, and wherein the controller is configured to compareattributes of the plurality of radiation emission readings to a libraryof flashes.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the radiation from at least two FOVs is superimposed toprovide a single high-resolution image, and wherein the controller isconfigured to determine the geolocation using information about a roughgeolocation obtained from the one or more photodetectors which providedthe radiation emission readings.

In accordance with an aspect of the presently disclosed subject matter,there is yet further provided a system comprising:

a frame buffer capable of memorizing a sequence of high-resolutionimages of a scene;

one or more photodetectors capable of obtaining radiation emissionreadings from the scene;

a controller is configured to detect a suspected flash event based onprocessing the radiation emission readings from the one or more photodetectors, wherein the detecting occurs at a first instant; and

wherein the controller is configured to retrieve from the bufferhigh-resolution images of the scene including at least one image thatwas captured prior to the first instant, and

wherein the controller is configured to process the high-resolutionimages of the scene to determine a geolocation of the suspected flashevent.

In addition to the above features, the system according to this aspectof the presently disclosed subject matter can optionally comprise one ormore of features listed below as different embodiments, in any desiredcombination or permutation.

In accordance with an embodiment of the presently disclosed subjectmatter, the system further comprises a high-resolution camera which isconfigured to capture the high-resolution images independently from thephotodetectors, and from a detection of a suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is configured to capture thehigh-resolution images continuously regardless of a detection of asuspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein at least one of the high-resolution images retrievedfrom the buffer precedes the appearance of the suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein a sampling rate of the photo detectors is higher thanthe frame rate of the high-resolution camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein a sampling rate of the photo detectors is at least 5times higher than the frame rate of the high-resolution camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photo detectors operate at a cut-off wavelengthwhich is higher than the cut-off wavelength of the high-resolutioncamera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the I-FOV of the high-resolution camera is at least 10times smaller in at least one axis than the FOV of at least one of theone or more photodetectors

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photodetector operates with a cut-off wavelengthwithin the extended SWIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera operates with a cut-offwavelength within the SWIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is adapted to captureradiation mainly within an atmospheric absorption hand.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera operates with a cut-offwavelength within the NIR range.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is a bolometric camera.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises spectral domain processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises intra-flash time-domain processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing the radiation emission readings from the oneor more photo detectors comprises total energy processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the spectral domain processing comprises processingradiation emission readings captured over a majority of a duration ofthe suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the intra-flash time-domain processing comprisesprocessing radiation emission readings captured over a majority of aduration of the suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the controller is further configured to determine basedon a processing of the radiation emission readings from the one or morephoto detectors, and based on a processing of the selected imageswhether the suspected flash event is an event of interest or not.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the controller is further configured to determine basedon a processing of the selected images whether the suspected flash eventis an event of interest or not.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein processing of the selected images comprises: spatialdomain processing and temporal-spatial processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is configured to have aninter-exposure interval that is shorter than the shortest possible pulseduration of a suspected flash event.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the high-resolution camera is configured to operate atwavelength band which is different from the wavelength band at which anyone of the photo detectors operate, and wherein said determining thegeolocation comprises cross wavelength band processing.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the photodetectors are adapted to obtain a plurality ofradiation emission readings during a flash duration, and wherein thecontroller is configured to compare attributes of the plurality ofradiation emission readings to a library of flashes.

In accordance with an embodiment of the presently disclosed subjectmatter, wherein the radiation from at least two FOVs is superimposed toprovide a single high-resolution image, and wherein the controller isconfigured to determine the geolocation using information about a roughgeolocation obtained from the one or more photo detectors which providedthe radiation emission readings from the scene.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, a preferred embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 is a functional block diagram illustration of a detection systemaccording to examples of the presently disclosed subject matter;

FIG. 2 presents a graph of spectral discrimination of a glint and anexample muzzle flash, and graphical illustrations of signal strength ofa glint and a muzzle flash detected by each of a silicon based detector,Indium gallium arsenide (InGaAs) detector and a Indium antimonide (InSb)detector, according to examples of the presently disclosed subjectmatter;

FIG. 3 is a functional block diagram illustration of one possibleimplementation of the detection system in FIG. 1, according to examplesof the presently disclosed subject matter;

FIG. 4 is a flowchart illustration of a detection method, according toexamples of the presently disclosed subject matter;

FIG. 5A illustrates a graphical illustration of images of a sceneretrieved in response to a detection of a suspected flash event,according to examples of the presently disclosed subject matter;

FIG. 5B illustrates a graphical illustration of images of a sceneretrieved in response to a detection of a suspected flash event,according to examples of the presently disclosed subject matter;

FIG. 6 is a flowchart illustration of the method according to FIG. 4 inone possible implementation according to examples of the presentlydisclosed subject matter;

FIG. 7 is a graphical illustration of an operational time line for adetection method, according to examples of the presently disclosedsubject matter;

FIG. 8 is a simplified functional block diagram of a photodetectorsarray and a camera array which can be used in a detection systemaccording to examples of the presently disclosed subject matter;

FIG. 9 is a functional block diagram illustration of a simplified blockdiagram of a photodetectors array and a camera array and a FOVcontroller; which can be used in a detection system according toexamples of the presently disclosed subject matter;

FIG. 10 is a functional block diagram illustration of one possibleimplementation of the system in FIG. 1, according to examples of thepresently disclosed subject matter; and

FIG. 11 is a flowchart illustration of a method of determining ageolocation of an optical event according to examples of the presentlydisclosed subject matter.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the presentlydisclosed subject matter. However, it will be understood by thoseskilled in the art that the presently disclosed subject matter may bepracticed without some of these specific details. In other instances,well-known methods, procedures and components have not been described indetail so as not to obscure the presently disclosed subject matter.

It is appreciated that, unless specifically stated otherwise, certainfeatures of the presently disclosed subject matter, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the presently disclosed subject matter, which are, forbrevity, described in the context of a single embodiment, may also beprovided separately or in any suitable sub-combination.

As used herein, the terms “example”, “for example,” “such as”, “forinstance” and variants thereof describe non-limiting embodiments of thepresently disclosed subject matter. Reference in the specification to“one case”, “some cases”, “other cases” or variants thereof means that aparticular feature, structure or characteristic described in connectionwith the embodiment(s) is included in at least one embodiment of thepresently disclosed subject matter. Thus the appearance of the phrase“one case”, “some cases”, “other cases” or variants thereof does notnecessarily refer to the same embodiment(s).

Unless specifically stated otherwise, as apparent from the followingdiscussions, it is appreciated that throughout the specificationdiscussions utilizing terms such as “processing”, “memorizing”,“detecting”, “configuring”, “selecting”, “retrieving”, “referencing”,“indexing”, “searching”, “receiving”, “storing” or the like, includeactions and/or processes of a computer that manipulate and/or transformdata into other data, said data represented as physical quantities,e.g., such as electronic quantities, and/or said data representing thephysical objects.

The terms “computer”, “processor”, and “controller” or the like shouldbe expansively construed to cover any kind of electronic device withdata processing capabilities, including, by way of non-limiting example,a personal computer, a server, a computing system, a communicationdevice, a processor (e.g. digital signal processor (DSP), amicrocontroller, a field programmable gate array (FPGA), an applicationspecific integrated circuit (ASIC), etc.), any other electroniccomputing device, and or any combination thereof.

The operations in accordance with the teachings herein may be performedby a computer specially constructed for the desired purposes or by ageneral purpose computer specially configured for the desired purpose bya computer program stored in a non-transitory computer readable storagemedium.

In embodiments of the presently disclosed subject matter, fewer, moreand/or different stages than those shown in FIG. may be executed. Inembodiments of the presently disclosed subject matter one or more stagesillustrated in FIGS. 4, 6 and 11 may be executed in a different orderand/or one or more groups of stages may be executed simultaneously.FIGS. 1, 3, 8, 9 and 10 illustrate different schematics of the systemarchitecture in accordance with an embodiment of the presently disclosedsubject matter. Functional elements in FIGS. 1, 3, 8, 9 and 10 can bemade up of any combination of software and hardware and/or firmware thatperforms the functions as defined and explained herein. In otherembodiments of the presently disclosed subject matter, the system mayoptionally comprise fewer, more, and/or different modules than thoseshown in FIGS. 1, 3, 8, 9 and 10.

A single optical detection unit, which is sometimes a pixel within alensed camera, has an Instantaneous Field Of View (IFOV) that collectsradiation from the clutter (which may include short spikes of signalsfrom sun glints and artificial sources), and from a flash if such existsin the IFOV. According to examples of the presently disclosed subjectmatter, distinguishing between the flash and the clutter may include acombination of some or all of the following criteria:

Spatial domain processing—a flash is almost always a sub-pixel event,which means that it accounts for a part of the IFOV. This means that theIFOV collects the collective radiation from the flash and the clutter.In some cases, the flash radiation may split between adjacent IFOVs, Asignal which appears on more adjacent IFOVs is usually not a flash,unless it is very close to the sensor so that the size of the flash isbigger than the IFOV, or very intense, thus causing internal sensorphenomena such as blooming which cause the signal to appear in IFOVswhich are not supposed to collect radiation from that flash.

Time-Spatial domain processing—this processing takes into account bothspatial and time dependent signals, usually video-type signals, toidentify movements such as birds flying, cars driving etc, in order toeliminate signals that appear to be flashes that appear on the course ofthe movements of these objects, but in fact result from the motion ofsuch objects in the field of view.

Intra-pulse time domain processing—by sampling the flash several timesduring its presence, one may compare the intensity-time function of theflash to a library of flashes, or compare several attributes of theshape to characteristic attributes of flashes. This requires samplingthe flash several times during its presence. This may be difficult if alarge (about 100,000 pixels) array of photodetectors is used. This isbecause the duration of a light arms muzzle flash is less than amillisecond. Sampling the flash ten times requires higher than 10,000Frames Per Second (FPS). This results in 1 Giga Pixel per second camerain the infrared (LWIR, MWIR or SWIR) or SBUV—which is far beyond today'savailable technology, and may certainly be bulky and expensive (seeanalysis in U.S. Pat. No. 8,304,729 to Snider). Note that therequirement for intra pulse time domain processing is 10 times higherthan the sampling rate required for the total flash energy analysis.This further excludes uncooled LWIR photodetector(s) for this purpose.

Spectral domain processing—the optical spectrum of flashes usually peaksbetween 3-5 microns. Sun glints are more powerful in the visible lightas the sun illumination peaks in the green wavelength, and diminish inpower with the increasing wavelength in the infrared. Comparing thesignal intensity in the infrared and visible, or between differentwavelength bands in the infrared or between the SBUV and otherwavelength bands helps distinguishing between flashes and sun glints andother radiation sources with different from flashes spectral attributes.(see U.S. Pat. No. 5,686,889)

According to an aspect of the presently disclosed subject matter, thereis provided a method which can be used for detecting an event ofinterest that is characterized by a predefined optical signature.According to examples of the presently disclosed subject matter, themethod can include: capturing images of a scene using a high-resolutioncamera, memorizing a sequence of high-resolution images of the scene,obtaining radiation emission readings front one or more photo detectors,processing the radiation emission readings from the one or more photodetectors for detecting radiation emission readings which correspond toa suspicious flash event, wherein detecting radiation emission readingswhich correspond to a suspicious flash event occurs at a first instant,and selecting from the sequence of high-resolution images of the sceneat least a first image which includes readings of radiation emissionfrom the detected suspicious flash event, and at least a second imagewhich includes readings of radiation emission which is notcharacteristic of the flash event, and wherein at least one of the firstor the second images was captured prior to the first instant.

According, to examples of the presently disclosed subject matter, themethod can further include determining at least based on the first andsecond images whether the suspicious flash event is an event of interestor not.

According to examples of the presently disclosed subject matter, themethod can further include determining the geolocation of the suspectedflash event at least based on the first and second images.

Reference is now made to FIG. 1, which is a block diagram illustrationof a detection system according to examples of the presently disclosedsubject matter. According to examples of the presently disclosed subjectmatter, the detection system 100 can include one or more photodetectorunits 10, one or more imaging units 20, a frame buffer 30, a processor40 and memory 50.

According to examples of the presently disclosed subject matter, thephotodetector(s) 10 are configured to detect a suspected flash event. Byway of example, the photodetector(s) 10 can include one or a plurality(e.g., two, three, . . . , n) of photo photodetectors. Thephotodetector(s) 10 can be a single band photodetector or a multipleband (e.g., band I and band II) photodetector or a multiple bandphotodetector array. According to examples of the presently disclosedsubject matter, the photodetectors can operate at a first band (band I)in which the appearance of solar radiation (used here as an example of anot-of-interest event) is relatively strong compared to the appearanceof solar radiation in the second band (band II), and in the second band(band II) the appearance of an event of interest is relatively strongcompared to the appearance of the event of interest in the first band(band I).

For example, the photodetector(s) 10 can be capable of operating in theextended short wave infrared band, and possibly also in the visibleand/or near infrared (“NIR”) bands. In further examples of the presentlydisclosed subject matter, the photodetector(s) can be capable ofdetecting or of providing radiation emission readings in the mid-waveinfrared (“MWIR”) or in the Solar Blind Ultra Violet (“SBUV”) bands.

It is noted that while SWIR photodetectors are usually less complex andless costly to implement in a flash detection system, compared to MWIRphotodetectors, MWIR photodetectors can typically achieve better Pd andFAR compared to SWIR photodetectors. In fact, in some cases, the Pd andFAR that can be typically achieved using SWIR photodetectors may beunacceptable for some flash detection applications. The choice ofphotodetector technology therefore depends on the characteristics offlashes to be detected, price sensitivity, power consumptionrequirements, performance requirements and detection system design. Someexamples of the detection and method disclosed herein take advantage ofa detection and geolocation algorithm (which can be implemented incontrol logic and executed by hardware components) that has thefollowing features:

A. A two phase detection process (more phases are also possible) thatincludes: a suspected flash event detection phase, and an event ofinterest validation phase (in which the initial, suspected flash event,is validated (or dismissed) and the geolocation of the event isdetermined);

B. The operation of the imaging unit (e.g., high-resolution camera),which is used in the event of interest validation phase is independentfrom the operation of the photodetectors, which are used in thesuspected flash event detection phase (and can also be used in the eventof interest validation phase). In particular, the high-resolution cameracan operate continuously and independently from the operation of thephotodetectors. The imaging unit has an inter-exposure interval that isshorter than the shortest possible pulse duration of an event ofinterest, and so there is effectively no risk that by the time theimaging unit is activated the flash will have already disappeared.

C. Continuous storage of images from the imaging in a buffer. Thestoring of images in the buffer is also independent from the operationof the photodetectors. The reading of images from the buffer is based onprocessing of samples from the photodetectors. Thus, images whichpredate the detection of the suspected flash event are available for usein the event of interest validation phase. In addition, images thatprecede and/or succeed the suspected flash event are available for usein the event of interest validation phase.

D. The processing of the samples from the photodetectors and thedetection of a suspected flash event provide a temporal reference (e.g.,including start time and duration of a suspected flash event) andpossibly also a rough spatial reference. The temporal reference, and ifprovided, the spatial reference, can be used to retrieve images from thebuffer and initiate an event of interest validation phase.

The inventors of the presently disclosed subject matter, have discoveredthat the above features enable a greater tolerance to low SCR, andsubsequently, a more favorable cost-to-performance tradeoff is madepossible. The greater low-SCR tolerance can provide flexibility in termsof the choice of technology which can be used in the flash detector.Thus, according to examples of the presently disclosed subject matter,SWIR photodetectors can be used for detecting suspected flash events.

It should also be noted that the use of SWIR and more particularly, thehigh frame rate which is more straightforward to achieve with un-cooledimaging unit (e.g., camera) technology such as InGaAs in the LatticeMatched SWIR band (or CMOS camera in the NIR) can also be regarded as afeature. When taking such a perspective, some of the detection andgeolocation algorithm features mentioned above, can be regarded as anoutcome of the high frame rate of the proposed un-cooled, high framerate, imaging unit.

There is now provided a description of certain features in examples ofthe presently disclosed subject matter that allow for more relaxedphotodetectors' SCR (per-sample) requirements, and thus provide greaterflexibility with respect to the choice of the type of photodetectorsthat can be used in the detection process.

According to examples of the presently disclosed subject matter, theimaging unit that produces the high-resolution images operatescontinuously and independently from the operation of the photodetectors.The images from the imaging unit are recorded in a buffer, and in case asuspicious flash event is detected by the photodetectors, two or moreimages are retrieved, where at least one of the images is retrieved fromthe buffer and at least one more image is retrieved either from thebuffer or directly from the camera. The term “buffer” is used here forconvenience only, and in some cases, the description makes a generalreference to the term “memory” when referring to the computer resourcethat is used for storing (or memorizing) an image that was taken by thetwo images. Thus, in this context, the tennis buffer and memory areinterchangeable.

The time budget that can be allocated for the provisional detection bythe photodetectors (the suspected flash event detection phase) is thussignificantly longer compared to a solution, where the photodetectorsact as a trigger for the imaging unit (such as in US20120001071),because the images are captured continuously and independently from theoperation of the photodetectors, and the imaging unit has aninter-exposure interval that is shorter than a pulse duration of anevent of interest, and so there is effectively no risk that by the timethe imaging unit is activated the flash will have already disappeared.For example, samples from the photodetectors which are collected over amajority of the duration of an optical event can be made available toand used by the suspected flash event detection algorithm to determinewhether an optical event is a suspected flash event or not. By way ofexample, the suspected flash event detection algorithm can obtain anduse samples from the photodetectors which cover the entire duration amajority of the duration) of the event and possibly also some timeafterwards or before the optical event. It would be appreciated, thatsuch information cannot be made available in a system that implemented atrigger-based imaging unit activation, where the decision to trigger theimager must be taken at the beginning of the event, so that the imagerto be triggered can still capture most of the event.

Furthermore, the samples from the photodetector(s) only provide aprovisional detection of a suspected flash event, and the conclusionthat a detected flash event is indeed an event of interest (or that itis a not-of-interest event) is based on assessment of processedhigh-resolution images (possibly in combination with an assessment ofthe photodetector(s) samples). In other words, according to examples ofthe presently disclosed subject matter, the data from thephotodetector(s) is augmented by processed images, and the processedimages are used to validate a provisional assessment (that is based onthe data from the photodetector(s)) that a certain optical event is asuspected flash event. For example, the analysis of the images from theimager can indicate the size of the event. An event which is captured bytoo many pixels is probably not an event of interest, and may bediscarded despite the detection by the photodetector. Additionalcriteria which can be used in the suspected flash event detection phaseshall be discussed below.

By way of example, the photodetector(s) 10 can include photodetector(s)that operate at a rate of between 2-20 kHz. The photodetector(s) can beconfigured to cover the system's 100 field of view (“FOV”) or at least apredefined portion of the system' 100 FOV, e.g., a majority of thesystem's 100 FOV. In a further example, the coverage of thephotodetector(s) can extend beyond the system's 100 FOV.

In the following description, for convenience and by way of example,reference is made to a single photodetector. However it should be notedthat a plurality of photodetectors can be used, and that any referencemade to a single photodetector applies to a multi-photodetectorimplementation, mutatis-mutandis.

Still in accordance with examples of the presently disclosed subjectmatter, the photodetector 10 can be adapted to operate in AC-coupledmode. Yet further by way of example, the photodetector diode area sizeand pixel FOV can be selected according to a link-budget parameter.

According to examples of the presently disclosed subject matter, thephotodetector 10 can include a single (one) pixel, or in other example,the photodetector can utilize more than one pixel (e.g., two, three, . .. , n pixels), but fewer than the number of pixels of an imaging unit 20as described below.

One or more optical elements can also be included or otherwise combinedwith the photodetector 10, including for example, a lens, a spectralfilter or a diffractive element. Furthermore, the photodetector 10 canalso include additional electronics, such as a band pass filter and apre-amplifier, AC coupler, bias subtraction, for example.

The signal from the photodetector(s) can be converted to a digitalsignal, and the digital signal can be processed to determine whether theradiation emission readings from the photodetector(s) correspond to asuspected flash event. Far example, the memory unit 50 can hold alibrary of signatures of events of interest. The signatures can take onmany forms. For example, each signature in the library can represent adifferent type of optical event (which is of interest).

The library can include various parameters about each of the flashes tobe detected, or about a group or groups of flashes which constitute asingle flash type in the library. For example, the library can holdsignatures of different 5.56 mm caliber weapons as a single flash typeor keep several 5.56 mm weapon signatures as separate entities.

The information stored about each flash source can include signatureduration, total energy, time dependent intensity shape, rise time, falltime, number of peaks, spectral contrast (total energy spectral ratio,or time-dependent ratio), and other attributes which may enable thealgorithm to distinguish between a flash and the background.

It would be appreciated that the detection of a suspected flash eventcan be performed entirely by the photodetector(s) 10, providing that thephotodetectors have appropriate independent processing capabilities, orin another example, the samples from the photodetector(s) 10 can beprocessed by an external processing device or unit, for example, theprocessor 40. It should be noted, that the detection of a suspectedflash event based on the photodetector's samples is a provisional stepin the detection process of an event of interest.

According to examples of the presently disclosed subject matter, thePhotodetector's 10 sampling rate is such, that the sampling duration isless than the duration of a suspected flash event or of an event ofinterest. Preferably, the photodetector's sampling rate enables toobtain several (e.g., 5-10) samples of the shortest event of interestwhich can be detected by the system 100. Since light-arms muzzle-flashduration can be as low as a few tens of a millisecond when measured inthe SWIR, sampling rate of 10-20 kHz can be a typical choice in a systemaccording to examples of the presently disclosed subject matter.

Throughout the description and in the claims reference is made to theterm “event of interest”. The term “event of interest” as used hereinrelates to a flash event whose appearance is characterized by asignature that has certain characteristics. According to furtherexamples of the presently disclosed subject matter, a signature of anevent of interest can be characterized by the appearance of a cloud ofhot gasses and particles, which appears at the moment of a projectile'slaunch, remains for a certain duration and dissolves. The temperature ofa flash varies between different types of flashes and with time. Ingeneral, the temperature is of the order of 1000° C. The cloud emitsradiation in the optical (muzzle-flash) and acoustic (muzzle-blast)domains. The optical radiation is distributed over the entire spectrum.It peaks in MWIR, as the blackbody radiation of the particle peaksthere, and is joined by CO₂ radiative gas relaxation. The radiationintensity diminishes but remains significant in the long part of theSWIR range (extended SWIR, 1.8-2.5 μm). The intensity declines with theshortening wavelength through the Lattice Matched SWIR, NIR, VIS andSBUV. In contrast, the solar energy increases with the wavelength fromgreen light to the MWIR. Therefore, VIS or NIR are preferred asreference wavelength bands to SWIR or MWIR: the SWIR and MWIR serve asthe prime detection hand, and the VIS or NIR are used to compare thesignal intensity (a reference detection band): in a flash event, thelonger wavelengths will be more powerful than the shorter, and viceversa for sun glints.

The duration of a flash varies among different flash types: light armsmuzzle flashes are relatively short: less than a millisecond. Rocketsand larger caliber guns can last several milliseconds to low hundreds ormilliseconds. The flash duration also varies with the wavelength band.In general, the shorter the wavelength, the shorter the flash duration.The short duration and low intensity of light arms muzzle flashes meansthat they are challenging to detect. Therefore, some of the examples inthis disclosure are focused on detection of light arms (the event ofinterest is a light arms muzzle flash).

Nonetheless, examples of the presently disclosed subject matter arecapable of detecting all relevant flashes in the environment. Byproviding appropriate suspected flash event criterion and event ofinterest criterion many types of flashes from various sources can bedetected using the examples of the presently disclosed subject matter.

FIG. 2 presents a graph of spectral discrimination of a glint and anexample muzzle flash, and graphical illustrations of signal strength ofa glint and a muzzle flash detected by each of a silicon based detector,Indium gallium arsenide (InGaAs) detector and a Indium antimonide (InSb)detector. Some or all of the detector types used in the illustration inFIG. 2 may be used in a detection system according to examples of thepresently disclosed subject matter, although other or additionaldetector types can also be used.

Throughout the description and in the claims, reference is made to theterm “suspected flash event”. The term “suspected flash event” as usedherein relates to an optical event whose appearance is characterized bya signature (that has certain characteristics). According to examples ofthe presently disclosed subject matter, an optical signature of asuspected flash event can be characterized at least by a certainduration. A suspected flash event according to examples of the presentlydisclosed subject matter, is an event whose, appearance is characterizedby a short appearance or a short duration optical signature. A suspectedflash event can be an event of interest or a not-of-interest event.

Examples of events which can be detected as suspected flash events,depending on the characteristics that are used to define a suspectedflash event, include: muzzle flashes from small arms, muzzle flashesfrom machine guns, muzzle flashes from artillery, muzzle flashes frommortars artillery or any other barrel based weapon, plume resulting fromthe launch of a missile or a rocket, sun glints, battlefield explosions,car-lights, car backfire, camera flash, campfire etc.

According to examples of the presently disclosed subject matter, theprocessor 40 can be configured, possibly using instructions that arestored in the memory 50 to apply a predetermined suspected flash eventcriterion to samples provided by the photodetector 10 to determinewhether a certain set of samples from the photodetectors indicate that asuspected flash event occurred. Further by way of example, in ease it isdetermined that a suspected flash event occurred, the processor 40 canbe configured, possibly using instructions that are stored in the memory50, to apply a predetermined event of interest criterion to at least twohigh-resolution images provided by the imaging unit 20, and possiblyalso to the samples from the photodetector 10, to determine whether asuspected flash event is an event of interest or not.

The suspected flash event criterion and the event of interest criterioncan be associated with certain characteristics of the suspected flashevent. According to examples of the presently disclosed subject matter,provisionally, a suspected flash event is detected according to a firstset of characteristics or attributes, and subsequently in case thesuspected flash event is found to be characterized by a second set ofcharacteristics or attributes, the flash event can be determined to bean event of interest (or a not-of-interest event). The first and thesecond sets of characteristics or attributes can include differentlevels of the same characteristics or attributes and/or altogetherdifferent/same characteristics or attributes. Examples of events whichcan be considered to be events of interest, depending on thecharacteristics or attributes that are used to define an event ofinterest and to configure the system 100, include: muzzle flashes fromsmall arms, muzzle flashes from machine guns, muzzle flashes fromartillery, muzzle flashes from mortars artillery or any other barrelbased weapon, plume resulting from the launch of a missile or a rocket.However, it would be appreciated that in other cases, the system can beconfigured to classify sun glints, battlefield explosions, car-lights,car backfire, camera flash, campfire etc., as “not-of-interest” events.It would be appreciated, that throughout the description and in theclaims, any reference that is made to an event of interest and tocharacteristics of such event can relate to a certain model, including acomputerized or digital model of such events. The model of an event ofinterest can include various digital representations of certaincharacteristics of measure, simulated or otherwise generated events.

The criteria that is used in the detection process can be implemented bythe processor 40. By way of example, the criteria can be stored in thememory unit 50 and can be utilized by the processor 40 to process thesamples from the photodetector 10 and from the imaging unit 20.

Muzzleflashes from light arms, machine guns, cannons, mortars, launchflashes of rockets and missiles etc, emit optical energy in a widewavelength band, typically peaking in the MWIR (3-5 microns), but stillsignificant in the SWIR, and further declining through the NIR, VIS andeventually the SBUV band.

In order to detect a flash with a high Probability of Detection (Pd),while maintaining low false alarm rate (FAR) a flash detection systemneeds to distinguish the flash from the background signal (clutter) andfrom the noise (system internal noise and shot noise). Distinguishingthe signal from the clutter requires sufficiently large Signal toClutter Ratio (SCR), and sufficiently large Signal to Noise Ratio (SNR).

Still further by way of example the flash detection process can includesome or all of the following criteria:

Total flash energy—aggregate the energy collected from the flash abovethe clutter, and generate a threshold. A flash can be more powerful thanother clutter related events, however, in some cases sun glints can bemore powerful than light arm muzzleflashes, and close sun glints canappear more powerful than far away flashes, even when the flashes arepowerful, such as rocket launch flash. Therefore, intensity relatedcriteria may not suffice in applications where low false alarm isrequired. The accurate measurement of flash energy is strongly dependenton clutter subtraction. The SCR strongly depends on the residual clutterthat remains after the subtraction. The SCR is mostly affected by theresolution, choice of spectrum and sampling rate—which is optimal whenintegration time is equal or shorter than flash duration. If integrationtime is longer than the flash duration, then it collects unnecessarytime-dependent clutter. Therefore, it is important that the integrationtime is as close as possible to the shortest flash to be detected.

Spatial domain—a flash can be assumed to be a sub-pixel event, whichmeans that it accounts for a part of the IFOV. This means that the IFOVcollects the collective radiation from the flash and the clutter. Insome cases, the flash radiation is split between adjacent IFOVs. Asignal which appears on more adjacent IFOVs can be assumed to not likelybe a flash. This analysis would usually be considered together withother criteria, since it is not conclusive evidence with respect to thenature of the detected optical event. For example, despite what wasdescribed above, under certain circumstances a flash may be manifestacross several IFOVs, e.g., when it occurs very close to the sensor sothat the size of the flash is bigger than the IFOV, or when the flash isvery intense, thus causing internal sensor phenomena such as bloomingwhich cause the signal to appear in IFOVs which are not supposed tocollect radiation from that flash.

Time-Spatial domain processing—this processing takes into account bothspatial and time dependent signals, usually video-type signals, toidentify movements such as birds flying, ears driving etc, in order toeliminate signals (optical events) that appear to be (suspected) flashevents, but in fact result from reflection that occurs while suchobjects are in motion within the field of view. When the reflectingobject is moving behind a chopping object (a grove of trees, or a fencefor example) the reflection can be modulated in a manner which appearsto the photodetectors, at least in some respects (e.g., energy vs. time)as if it were a flash event (or an event of interest). Typically,time-Spatial domain processing such as a motion tracking algorithm canbe effective for detecting a moving object in the field of view,attribute the suspected flash event to the moving object, and determineit to be a not-of-interest event. It would be appreciated that suchtime-Spatial domain processing may require high-speed (with respect tothe flash duration, i.e., the inter-exposure interval is shorter than apulse duration of an event of interest) video stream with multiple(e.g., tens to hundreds) frames in order to be effective.

Intra-pulse time domain processing—by sampling the flash several timesduring its presence, the intensity-time function of the flash can becompared, for example, to a library of flashes, or the intensity-timefunction of the flash can be compared to one or more attributes of theshape intensity time function of the optical event to characteristic(pre-stored) attributes of events) of interest. Such processing requiressampling the optical event several times during its presence. Whenconsidering some types of flash events which can be of interest,sampling rate of this magnitude can be difficult to achieve if a large(about 100,000 pixels) array camera is used. For example, the durationof a light arms muzzleflash is less than a millisecond, and sampling theflash ten times would require a frame rate that is higher than 10,000Frames Per Second (FPS). This results in 1 Giga Pixel per second camerain the infrared (LWIR, MWIR or SWIR) or SBUV—which is beyond today'savailable technology, and will likely be bulky and expensive (see forexample a similar analysis provided in U.S. Pat. No. 8,304,729 toSnider). Note that the requirement for intra pulse time domainprocessing is 10 times higher than the sampling rate required for thetotal flash energy analysis. This further excludes uncooled LWIRphotodetectors for this purpose due to such photodetectors' longintegration time (in the order of 10 milliseconds). Therefore, therequirement for sampling a light arms muzzle flash several times iscontradictory to the requirement for spatial processing, and to therequirement for providing accurate bearing towards the flash, becausehigh sampling rate reduces resolution.

Spectral domain processing—the optical spectrum of flashes usually peakbetween 3-5 microns, and decline with the wavelength. Sun glints aremore powerful in the visible Light as the sun illumination peaks in thegreen wavelength, and diminishes in power with the increasing wavelengthin the infrared. Comparing the signal intensity in the infrared andvisible bands or between different wavelength bands in the infrared orbetween the SBUV and other wavelength bands helps distinguishing betweenflashes and sun glints and other radiation sources which are differentfrom flashes' spectral attributes. (see U.S. Pat. No. 5,686,889)

According to examples of the presently disclosed subject matter, theimaging units) 20 includes one or more high resolution camera(s). Forconvenience, reference made in the present disclosure to an imaging unitor to a camera (in the singular form) may also refer to animplementation where multiple imaging units or multiple cameras,respectively, are used in the detection system, unless explicitly statedor implicitly apparent (from the context) otherwise.

Further by way of example, the high-resolution camera can have an arrayof more than 10,000 pixels, or, preferably more than 100,000, in orderto enable sub degree of angular resolution. For example: a 256×320 arraywhich images a 100 degrees of angle horizontal FOV can yield an accuracyof 100/320≅⅓ degree of angle. This angular accuracy can be sufficientfor identifying the specific shooter, as it presents approximately 2 merror in a light-arms effective range of 300 m. Further by way ofexample, the high-resolution camera can be characterized by aninter-exposure interval that is shorter that a pulse duration of anevent of interest. The camera can operate in a wavelength of highsensitivity to the flash, but can also work in a spectrum range that isless optimal than the spectrum used for the photodetectors. According toexamples of the presently disclosed subject matter, the camera caninclude any one or any combination of the following: Lattice MatchedSWIR (In_(0.53)Ga_(0.47)As), Extended SWIR detectors (strained InGaAs,MCT, PbS Superlattice, etc), or un-cooled bolometric cameras or MWIRdetectors such as cooled InSb or cooled MCT and others. The frame rateof an infrared (SWIR or camera with over 10,000 pixels is typicallylimited to 100 s of FPS (Frames Per Second). Particularly fast camerasmay be as fast as 2000 FPS full frame, which results in integration timeof 0.5 msec. Even at this high frame rate, the frame time is longer thanthe small caliber light arms muzzle-flash. Since the photodiode samplesthe flash multiple times, it already provides the time-dependentsignature of the event. Therefore, there is no necessity for the imagerto provide several images within the flash duration.

According to examples of the presently disclosed subject matter, imagingunit 20 is capable of operating with an inter-exposure interval that isshorter than a pulse duration of an event of interest. Theinter-exposure interval of the imaging unit 20 is such that it is shortenough so that the pulse does not occur within the inter-exposureinterval (and could be missed by the imaging unit 20).

Furthermore, according to examples of the presently disclosed subjectmatter, the imaging unit is capable of operating at a frame rate whichyields a frame time (which is equal to the sum of the exposure time andthe inter-exposure interval) that is approximately equal (e.g., as closeas possible) to the (estimated) duration of a shortest event ofinterest. The closer the integration time of the imager to the shortestflash duration, the lower the clutter that will be collected (because asmaller portion of the radiation is collected while the signal from theflash is not present), and the signal to clutter ratio will improve.This improvement will stop at the point when the imager frame time willbe about half the shortest flash duration. In this case, at least in oneframe, the integration time will be contained within the flash duration,achieving a better signal to clutter ratio relative to the case of alonger frame time. Since increasing the frame time is technicallydifficult and costly, it makes sense to increase it only up to the pointwhere the signal to clutter peaks at the imager or meets a certainthreshold (if less, than the optimal result is acceptable), and collectthe time-dependent signature using the low resolution photodetectors.

According to examples of the presently disclosed subject matter, theimaging unit includes, a non-cryogenically cooled infrared detectorsarray, including for example any one of: CMOS, CCD NIR orlattice-matched InGaAs, Extended-SWIR InGaAs, Extended-SWIR MCT, PbS,PbSe or bolometric detectors. Bolometric detectors are intrinsicallylimited to long integration times of several milliseconds. Therefore,they are not suitable for gunfire detection applications, but remainrelevant for longer flashes such as in the case of antitank missilelaunch and mortar fire, which in some examples of the presentlydisclosed subject can be the types of optical events which are ofinterest. Cryogenically cooled array detectors can be difficult tooperate at high frame rates, such as those required from the imagingunit according to examples of the presently disclosed subject matter. Atleast in part, this is due to the heat generated by the array detectorsand excess heat conductivity generated by the extra communication lines.The heat buildup and the need to provide a large cooling capacity by thecryogenic cooler to deal with it, increases its cost and size, if thisis at all possible. Suitable detectors for gunfire detection which alsopresent a good cost-performance ratio are lattice-matched SWIRdetectors, and mostly such that are configured to utilize theatmospheric absorption bands (see for example U.S. Patent ApplicationPublication No. 2011/0170798 to Tidhar). Extended SWIR detectors mayalso be useful as such sensors provide good signal to clutter ratiowhile maintaining intermediate cooling requirements compared to thecooled infrared detectors in the MWIR band. NIR imagers are the mostcommercially available, have lowest cost, highest frame-rate and highestresolution. With careful choice of sub-bands in the NIR, NIR imagerspresent a cost effective choice of imagers, mainly for larger caliberapplications where the signal is significant also in the NIR. Achallenge in a NIR detection system is avoiding false alarms—but in somesettings, the false alarms can be eliminated to some extent by thephotodetectors, enabling an effective use of NIR imagers for primarilylocating, rather than detecting and discriminating optical events ofinterest, as done in prior art systems.

According to examples of the presently disclosed subject matter, theimaging unit 20 can be configured to capture images (or frames)independently of the operation of the photodetector 10 and the samplesgenerated by the photodetector 10. Still further by way of example theimaging unit 20 can be configured to capture images (or frames)continuously. The images can be captured one after the other with onlyan inter-exposure interval in between pairs of consecutive images. Theimages can be captured as long as the system 100 is in active mode. Theimages can be kept in the frame buffer 30, and the buffer can store theimages and overwrite older images, as necessary, according to apredefined images buffering scheme.

According to examples of the presently disclosed subject matter, theframe buffer 30 can be capable of temporarily storing a certain numberof images that were captured by the imaging unit 20, or the frame buffer30 can have a certain capacity which corresponds to some number ofimages that can be stored thereon. According to further examples of thepresently disclosed subject matter, the capacity of the frame buffer 30can be sufficiently large so as to allow for the storage of at least oneimage that completely precedes an event of interest, at least one imagethat was captured during the event of interest and at least one imagethat was captured after the flash from the event of interest hasdecayed. In further examples of the presently disclosed subject matter,the buffer 30 can be large enough to store all images taken within aduration that extends between the beginning of the longest event ofinterest to the time it takes to determine based on the photodetectorthat a suspected flash event has occurred. For example, assuming a 50msec flash, and 30 msec for the photodetector and its respectiveprocessing to decide that a suspected flash event has occurred, if theframe time of the camera is 1 msec, then at least 80 frames can bestored. If the detection process is configured to use frames whichpredate a detected suspected flash event, the buffer 30 capacity can beextended further to enable storage of a certain (e.g., predefined) framewhich precedes the instant of the detected suspected flash event.

According to examples of the presently disclosed subject matter, thesystem 100 can be configured to detect a plurality of suspected flashevents simultaneously within the same imager, and to determine which, ifany, of the plurality of detected suspected flash events is/are an eventof interest. According to examples of the presently disclosed subjectmatter, the frame buffer 30 can have a capacity which supports multiplesuspected flash event detection and validation. The exact size of theframe buffer 30 can be a design choice.

According to examples of the presently disclosed subject matter, as willbe further described below, motion analysis algorithms can beimplemented by the processor 40 as part of the process of determiningwhether a detected suspected flash event is an event of interest.Various motion analysis algorithms are known in the art and can beimplemented herein, including optical flow, and motion analysisalgorithms that are used in standard video compression algorithms suchas MPEG, H.264, and others. It would be appreciated, that in order tocreate a reliable motion vector, the ability according to examples ofthe presently disclosed subject matter to use images that were takenbefore the start of the suspected flash event, can contribute to thereliability and usability of the motion analysis.

According to examples of the presently disclosed subject matter, in casemotion analysis algorithms are used as part of determining whether asuspected flash event is an event of interest or not, the frame buffer30 can have a size that is sufficient to store the number of frames thatis required for motion analysis. This number can be determined accordingto some predefined motion model or models. Motion analysis can be usedto accurately subtract the background from the images which include theflash, according to the motion at the location of the flash event in theframe, and, in some cases, avoiding the need for a navigation system fordetermining the motion. It can also be used to attribute long-lastingflashes from different pixels to the same event according to the localmotion at the specific area.

By way of example, the frame buffer 30 can be configured to supportdetection of hundreds of suspected flash events, or typically 1second=1000 frames, assuming 320×256 pixels×2 Bytes/pixels×1000events=164 MByte. As long as the photodetector can distinguish theoptical events within its field of view, the optical events can also bedistinguished in the imager. This is unlike systems that use thephotodetector as a trigger for the imager.

According to examples of the presently disclosed subject matter, theframe buffer 30 includes computer readable memory, such as NVRAM, RAM,ROM, EEPROM, flash memory or other suitable data retention, memory orstorage technology.

According to examples of the presently disclosed subject matter, theprocessor 40 can be configured to control the detection system 100. Theprocessor 40 can also control or assist in controlling any component ofthe system 100 or certain operations which are implemented in acomponent of the system. Still further by way of example, the processor40 can include a processor, a microprocessor, a microcontroller, a fieldprogrammable arrays (FPGA), application-specific integrated circuit(ASIC), etc.

By way of example, in addition to the frame buffer 30, the detectionsystem 100 can include memory 50. Still further by way of example, thememory 50 can be configured to store digital data, programs,executables, code, statistics, parameters, libraries (e.g., temporaland/or spectral signature libraries, libraries of trajectories,libraries of spatial signatures mostly—for cases of launch from a closerange), characteristics and/or other relevant information which isnecessary for or used in the operation of the detection system 100 orany of its components. One or more of the components of the detectionsystem 100 can access the memory 50 in utilizing the programs, data,libraries, and/or other information, and/or for storing data. The memory50 can include volatile and nonvolatile, removable and non-removablemedia implemented in substantially any relevant method or technology fordata retention such as computer readable instructions, data structures,program modules or other data. For example, the memory can include, butis not limited to, NVRAM, RAM, ROM, EEPROM, flash memory or other memorytechnology, CD-ROM, digital video disk (DVD) or other optical diskstorage, magnetic cassettes, magnetic disk storage or other magneticstorage devices, or any other tangible medium which can be used to storethe desired information and which can be accessed by the components ofthe detection system 100. In addition or alternatively, the memory 50can be included in one or more of the other components of the detectionsystem 100.

The detection system 10 and/or a component of the detection system 10can be implemented in hardware or a combination of hardware andsoftware.

Reference is now made to FIG. 3, which is a block diagram illustrationof one possible implementation of the detection system in FIG. 1,according to examples of the presently disclosed subject matter. By wayof example, the detector system 300 includes two arrays ofphotodetectors: a MWIR or SWIR photodetectors array 310 and a VIS or NIRphotodetectors array 320. The detector system 300 can include forexample, a SWIR camera 330, which is capable of producing hi-speed andhigh-resolution images, for example, the SWIR camera 330 shoots adigital video stream. The SWIR provides geolocation and validation forof all calibers without the need for cryogenically cooling. Alternativesto SWIR camera include for example: NIR which low cost; bolometric whichprovides night-vision capability; MWIR which is cryogenically cooled.The camera 330 is functionally independent from the operation of thephotodetector arrays 310 and 320.

Further by way of example, photodetector arrays 310 and 320 areoperatively connected to an analog to digital convertor and artamplifier 340 array, which generate an amplified and digitized signalfrom the photodetector samples. A microcontroller 350 streams thedigital samples from the photodetectors together with timestamps foreach sample and possibly also spatial reference indicators (to indicateFOV is covered by each sample). The microcontroller 350 can also beconfigured to control the currents, power and calibration of thephotodetectors, and can be configured to communicate with the centralcontroller and processor of the system. The microcontroller 350 can alsobe configured to provide time-synchronization with and between the othercomponents of the system (all or some of which), in some configurations,the microcontroller 350 can be configured to perform the initialdetection function, which in FIG. 3 appears in block 370.

Still further by way of example, the images from the SWIR (or NIR)camera 330 are fed to a FIFO buffer 360, e.g., over a digital videocamera link. Each frame from the SWIR (or NIR) camera 330 includes atimestamp that indicates the time at which the frame was captured.Possibly, with each frame there is also provided a spatial referenceindicator which indicates which FOV is covered by the image. Thetimestamp and spatial reference indicator can be stored in the FIFOmemory 360, possibly in a way that facilitates quick access to images inthe buffer according to a given timestamp and/or according to a givenspatial reference indication. For example, tables indexes and othersuitable data structures can be used for indexing and accessing theframes in the FIFO memory 360. Since the spatial reference does notchange frequently, it can be calibrated and stored in a differentlocation, and be re-calibrated and re-entered to the system only when aphotodetector or a camera is replaced or in any other predefined event.

According, to examples of the presently disclosed subject matter, aprocessor 370 receives (either by push or pull) the photodetectorsamples stream and processes the samples, e.g., using a predefinedsuspected flash event criterion (time dependent intensity,time-dependent spectral ratio etc.), to determine whether thephotodetector samples at a certain period of time, and possibly also ata certain bearing (relative to a given reference point) are indicativeof a suspected flash event. For illustration purposes, the suspectedflash event detection process which is implemented by the processor 370is depicted by block 372.

According to examples of the presently disclosed subject matter, in casethe processor 370 determines that the photodetector samples indicate asuspected flash event, the processor 370 determines a time and aninitial spatial reference of the suspected flash event according to theFOV covered by the photodetector. According to some examples of thepresently disclosed subject matter, the processor can determine aduration of the suspected flash even, the time when it started (e.g.,using a time reference or index, or a clock count), classification ofthe source of the flash (which type of weapon was launched), a magnitudeof the flash event (which, with the knowledge of the weapon type canenable rough estimation of the range), level of certainty, and otherparameters.

According to examples of the presently disclosed subject matter,following a detection of a suspected flash event and extraction of atime and possibly also a initial spatial reference of the suspectedflash event, the processor determines an image number and possibly arelevant scene sub-area according to the time, duration and geolocationdata front the photodetector samples which were identified to beindicative of a suspected flash event. For illustration purposes, thephotodetector samples to images cross referencing process is depicted byblock 374.

According to examples of the presently disclosed subject matter, theprocessor 370 then retrieves from the FIFO buffer 360 the image whichmatches the image number of the sub-area. This process can be repeatedfor several images, or the processor can simply retrieve a plurality ofimages which correspond to the suspected flash event. The selection ofwhich images to retrieve from the FIFO buffer 360 can be based onvarious algorithms and logic which can be implemented by the processor370.

Some examples of selection criteria which can be used by the processor370 include: take a certain number of images from the buffer, where atleast one image is an image that was captured before the start of thesuspected flash event; take as many images that were taken during theoccurrence of the suspected flash event as possible plus a certainnumber of images before the start of the event, and possibly also, acertain number of images that were taken after the event ended.

Further by way of example, the processor 370 can select the images thatare to be retrieved from the FIFO buffer 360 according to the spatialinformation that is provided with (or is otherwise associated with) thephotodetector samples and/or according to the spatial information thatis provided with (or is otherwise associated with) the buffered images.

According to examples of the presently disclosed subject matter, theprocessor 370 can be configured to calculate a geolocation of the eventof interest based on the processing of the retrieved images, by locatingthe pixel which best matches the suspected flash that was detected bythe photodetectors. For example: the photodetectors indicate that thereis a suspected flash at a given time, with a given duration at a givensub-area of the images from one of the cameras. The images, which wereretrieved according to the data from the photodetectors are supposed toinclude the optical signature of the suspected flash event, areprocessed with images, which according to the data from thephotodetectors, are not supposed to include the optical signature of thesuspected flash event (the latter group of images serves chiefly as abasis for subtracting the background from the images which include theoptical signature of the suspected flash event). In the difference imageor images (in case of a flash that is longer than a single frame time),a processing stage can be implemented for locating a pixel (or a groupof adjacent pixels, typically 1-4 pixels) which best matches thesignature of the suspected Hash event as measured by thephotodetector(s). In this context, a best match can relate to: a pixelreading value (indicating a highest energy reading with respect to otherpixels and/or with respect to readings from the photodetector), aduration of the suspected flash event, a size of the suspected flashevent signature (for example, if the signature is represented by morethan a predefined number of pixels, or it has a non-compliant spatialshape, or its in-pixel time-dependent signature does not match thesignature as read by the photodetector, the suspected flash event can bedisqualified, or another pixel having a better match may be selected asthe pixel where the flash event of interest occurred).

As mentioned above, according to some examples of the presentlydisclosed subject matter, the validation phase can include both avalidation function and a geolocation function. The pixel that wasselected as part of the validation function, as mentioned above, canserve the geolocation function. Each pixel in the image (or images)captures radiation from a different direction bearing with respect tothe imager's orientation (also known as a mechanical reference of thesystem). Thus, once it is determined which pixel captured the radiationfrom the event of interest, the bearing to the event of interest isdetermined. Inertial measurement unit (“IMU”) and/or GPS can be used toprovide a global azimuth and elevation with respect to the geographiclocation (rather than the system mechanical reference) to the event ofinterest.

According to some examples, in case more than one pixel (a group ofadjacent pixels) is selected during the validation function, then thebearing to the event of interest can be calculated as a weighted averageor any other kind of average of the bearing of the pixels that wereselected.

Further by way of example: in case the images were taken from a movingvehicle, the areas in the image that are closer to the vehicle move at ahigher pixels/frame rate than those from further areas. A motionanalysis algorithm can be used to segment the images to small blocks,and assign a motion vector to each block based on cross correlation orsimilar algorithms. The images without the suspected flash can besubtracted from the images with the flash using a block-by-block motioncorrection, and the relevant background in each area within the imagemay also be subtracted. This process can significantly improve thesignal to clutter ratio in the imager, improving the probability tolocate within the images the suspected flash that was detected by thephotodetector. After properly subtracting the background from the imageswhich include the optical event that is considered to be the suspectedflash event, the area in the image (e.g., a pixel or a group ofneighboring pixels) which best matched the suspected flash eventdetected by the photodetector can be processed to determine whether thesuspected flash event is an event of interest (or not). The specificpixel (or neighboring pixels) in the image where this suspected flashevent was found is directly related to the geolocation of the event.According to examples of the presently disclosed subject matter, theangular geolocation of the event of interest can be determined. It wouldbe appreciated that in some examples of the presently disclosed subjectmatter, the geolocation of the optical event (which can be an event ofinterest) can be determined directly from the images, and without usingor relying on an inertial measurement unit (“IMU”) or a similar devicefor subtracting the background from the image. Moreover, the ability touse motion vectors, based on the images from before the suspected event,and based on the independent high-frame-rate image capture, can enhancethe signal to clutter ratio at the imager, enabling the use of lowercost imagers using wavelength bands which are commonly considered to beinferior to MWIR bands for this application (such as using InGaAsdetectors in the SWIR or CMOS detectors in the NIR or bolometricdetectors instead of cooled InSb detectors in MWIR).

In further examples, the processor 370 can process the images that wereretrieved from the FIFO buffer to determine whether the suspected flashevent is an event of interest or not. According to examples of thepresently disclosed subject matter, the processor 370 can be configuredto carry out various motion processing operations to detect and analyzethe optical event in the images (or the lack thereof), and the processorcan apply various events of interest criteria to determine, based on theprocessed images, whether the suspected flash event is an event ofinterest or not. For example: one of the problems of detection systemsis detection of false flashes which are caused by glints (e.g., sunglints) from moving objects, such as cars or birds. A tracking algorithmmay be used to track moving objects appearing in a sequence of images,and advantageously the sequence of images would include images takenbefore and after the occurrence of the flash event. Such a trackingalgorithm, supported by a plurality of images which include the movingobject, can be used to disqualify suspected flashes which are not ofinterest.

Another example of a manner by which the processor 370 can use theavailability of the images and their use to validate a suspected flashevent (as an event of interest) is the following: in ease, as in someexamples of the presently disclosed subject matter, the imagers work ina spectral band that is different from the spectral bands of thephotodetectors, the images can provide additional spectral informationthat can be used (by the processor) to confirm or reject the originalspectral analysis based on the spectral bands of the photodetectors.

In yet another example of an attribute of the images and its use in theflash detection process: in most eases of interest, the flash capturesan angle smaller than the IFOV. Therefore, its radiation should becaptured by 1, 2, or 4 pixels, depending on its location with respect tothe edges between the pixels, and depending on the Point Spread Function(PSF) of the optical system. In case the flash radiation is detected bymore than four pixels, it may indicate an event which is too large for aflash (and may result from another source of radiation) or it mayindicate a very close flash. These cases cannot be resolved based on thedata from the photodetectors alone, because the photodetectors lack thespatial resolution that the imagers have. Accordingly, in some examplesof the presently disclosed subject matter, during the validation phase,the images can be processed to validate or disqualify suspected flashevent indications.

Yet another example of the use of data from the images to validate asuspected flash detection and possibly to determine a geolocation of anevent of interest (or to improve the process of determining thegeolocation of the event of interest): in case an event of interest islonger than the frame time of the imager, several images may includeradiation readings from the optical event. In such a case, atime-dependent signature may be generated from the images which includethe radiation readings. As part of the validation phase (which possiblyincludes also a geolocation process), the time-dependent signature canbe compared with the signature captured by the photodetectors, in orderto validate the detection or to better choose the pixels in which theflash was captured.

For illustration purposes, the process of validating a suspected flashevent as an event of interest (or determining that it is a not ofinterest event) which is implemented by the processor 370 is depicted byblock 376.

According to examples of the presently disclosed subject matter, thesystem 300 can be configured to communicate, externally, informationwith regard to the optical event, in particular, with regard to anoptical event which was determined to be an event of interest. To thisend the system can include a transmitter or a transceiver (neither areshown in FIG. 3) and any necessary interfaces, antenna or any otherdevice or component. The information with regard to the optical eventcan include: an alert in ease the event was determined to be an event ofinterest, geolocation of the event, classification of the type of sourcewhich caused the optical event, timestamp, estimated range, certainlylevel, etc. In some examples of the presently disclosed subject matter,the system 300 can also be configured to receive data, including forexample configuration data, including data which configured thesuspected flash event criterion and/or the event of interest criterion,information about the range map of the field of view, indication from anexternal source about a suspicious event (e.g. a radar) etc.

Additional reference is now made to FIG. 4, which is a flowchartillustration of a detection method, according to examples of thepresently disclosed subject matter. In the following description ofdetection method illustrated in FIG. 4, reference is made to thedetection system 100 and its various components which are shown in FIG.1, and which were described above with reference to FIG. 1. It should beappreciated however, that the detection method according to examples ofthe presently disclosed subject matter, is not necessarily limited tobeing applied to detection system 100, and other detection systemdesigns and configurations earl be used in conjunction with thedetection method according to examples of the presently disclosedsubject matter.

According to examples of the presently disclosed subject matter, as amatter of routine, images of a scene can be captured using an imagingunit (block 405). The images captured by the imaging unit can bememorized in a frame buffer (block 410). The capturing and memorizingblocks cart be implemented continuously, e.g., the imaging unit canoperate in a video or video-like mode,

According to examples of the presently disclosed subject matter,independently of the operations described in block 405 and 410, a scenecan be monitored using a photodetector which provides a sample durationthat is not greater than a suspected flash event duration (block 415).In a specific example, the sample duration is a fraction (e.g., apredefined fraction) of the shortest flash event duration of interest,so that, for example, five or more samples of the scene can be obtainedduring an event of interest (which would be recognized initially as asuspected flash event). By way of example: if the flash event ofinterest is light-arms muzzleflash, whose duration is 0.5-1 msec, thenthe sample duration of choice may be around 0.05-0.2 millisecond. Thescene which is monitored by the high sampling rate photodetectors canoverlap with the scene that is imaged by the imaging units, althoughthese two scenes may not necessarily be fully overlapping. Typically,several photodetectors cover the field of view of each imaging unit. Amapping among each photodetector and corresponding regions in the FOV ofeach imager can be kept by the system, and can be used during validationphase.

The samples from the photodetector 10 can be processed (block 420). Forexample, a sample can be compared to a predefined suspected flash eventcriterion. Further by way of example, a prestored signature bank can bestored in the memory unit 50, and the processor 40 can compute across-correlation between the time-dependent signatures from thesignature bank and the signal (radiation emission vs. time readings)from the photodetector 10. In yet further examples, the processor canuse wavelets analysis, heuristic analysis or any other processing of thesignals to determine if the signals correspond to a suspected flashevent signature. By way of further example, the processor can computethe spectral ratio vs. time of the readings from photodetectors ofdifferent wavelength bands with overlapping field of views, anddetermine whether this time-dependent or total spectral ratiocorresponds to a suspected flash event. The suspected flash eventdetection phase can include pre-processing functions, such as backgroundsubtraction (for example, by using AC coupling, bias subtraction andother methods).

According to examples of the presently disclosed subject matter, in caseit is found that a certain sample includes radiation emission readingswhich are indicative, e.g., according to the suspected flash eventcriterion, to a suspected flash event (block 425), images from the framebuffer 30 can be selected to determine whether the suspected flash eventis an event of interest or not.

According, to some examples of the presently disclosed subject matter,if a sample which includes radiation emission readings which areindicative of a suspected flash event is identified, a first image whichincludes radiation readings from the detected suspicious flash event anda second image which includes radiation readings which are notcharacteristic of the flash event can be obtained from the buffer 30,where at least one of first and the second images was captured prior tothe suspected flash event identification (block 430).

According to examples of the presently disclosed subject matter, atleast one of the images retrieved from the buffer includes a signatureof the suspected flash event, and at least one other image from theimages retrieved from the buffer does not have the signature of thesuspected flash event in it (e.g., it was taken before or after thesuspected flash event). Further by way of example, the image which doesnot have the signature of the suspected flash event can be an imagewhich precedes or supersedes the flash event.

According to examples of the presently disclosed subject matter, thetiming of the samples from the photodetectors and the timing of theimages captured by the imaging system may be cross-correlated. Forexample, a system clock can be used to time-index the samples and theimages. Based on the processing of the samples from the photodetectors,time-indexes can be determined for the retrieval of images from thebuffer.

According to further examples of the presently disclosed subject matter,in ease the FOV of the photodetector is smaller than the FOV of theimaging unit 20, only the portions of the images that overlap the FOV ofthe photodetector 10 which indicated a suspected flash event will beselected. This can occur, for example, when an array of photodetectorsis used for detecting a suspected flash event, and when the suspectedflash event is detected by one (or by some) of the photodetectors in thearray. In such a case, a predefined spatial referencing can bepredefined in the system to allow the system to determine which portionof an image or of images correspond to the FOV of a given photodetectorfrom the array of photodetectors.

The images that were retrieved from the buffer can be processed todetermine whether the signature (or signatures) of the suspected flashevent meets a predefined event of interest signature criterion. Furtherby way of example, a prestored signature bank can be stored in thememory unit 50 possibly together with additional criteria, and theprocessor 40 can compute a cross-correlation between the signatures fromthe signature hank and the images that were retrieved from the buffer.Examples of the image processing operations which can be included in thevalidation phase were described above.

The processor 40 can perform any other suitable computations andprocessing operations with respect to the images that were retrievedfrom the buffer and using any other suitable criteria to determinewhether the suspected flash event is an event of interest or not.According to examples of the presently disclosed subject matter, theprocessor can be configured to process the images that were retrievedfrom the buffer and to implement motion analysis algorithms such asoptical flow to assess the relative motion between the system and thelocal area which includes the suspected flash, to enable precisebackground subtraction. In addition, the algorithm can identify movingobjects in the area of interest, which are capable of generating falseflashes. Such false flashes may be classified as suspected flash events,which are subsequently, following the validation phase, disqualified asnot-of-interest events.

For example, referring now to FIG. 5A, there is shown a graphicalillustration of images of a scene retrieved in response to detection ofa suspected flash event. As can be seen in FIG. 5A, image 510 (cameraexposure 101) shows a road 512, a truck 514 on the road and a house 516and trees 518 and 519, where tree 518 is closer to the system than tree519. Image 520 (camera exposure 103) shows the same road 512, truck 514,house 516 and trees 518 and 519 from image 510, possibly the relativelocation and/or the relative size of at least some of which has changed,e.g., due to movement, and also possibly the location within the frameof some of the objects also shifted, e.g., due to panning or motion ofthe system.

Also apparent in image 520 is a flash 525 from a gunshot. For the sakeof illustration, it is assumed that some time after the flash 525occurred, the flash 525 is identified to be a suspected flash, event,and subsequently an event of interest. In image 530 (camera exposure105) the same road 512, truck 514, house 516 and tree 519 from images510 and 520 are shown, but in this image the closer tree (518) hasdrilled outside the frame.

Such possible perspective and relative size changes, for example, due todifferent angular motion of objects in the scene, should be coped within an efficient manner. For example, when the system is in motion, therelative size and/or the relative location of different objects in thescene cart change between frames as a result of different ranges betweenthe system and the various objects in the scene. In another example, therelative size and/or the relative location of different objects in thescene can change between frames as a result of motion of objects in thescene.

Thus for example, in FIG. 5A, subtracting the truck requiresidentification of the truck in each of the images and implementing amotion vector calculation. It should be rioted that global motionestimation and compensation may not be sufficient and may result infalse detection as a result of motion in the images.

Reference is now made to FIG. 5B, where there is shown a graphicalillustration of images of a scene retrieved in response to detection ofa suspected flash event. As can be seen in FIG. 5B, in image 550 and inimage 560 the truck 552 reflects the sun and a glint is picked up by thephotodetectors. The truck 552 travels behind the trees 528, which maycause the sun-glint 562 to modulate so that it is captured by thephotodetectors as if it were a flash (the detector identifies themodulated glint from the truck as a suspected flash event), it would beappreciated that detection of certain types of glints as a suspectedflash event can be prevented at least to a certain extent byimplementing a complex criteria for discerning a suspected flash eventas mentioned above, for example, spectral domain and time domainprocessing can be used to eliminate false positives to some extent.False positive detection of suspected flash events can be furtherreduced by implementing temporal spatial processing, such as objectmotion tracking. For example, in FIG. 5B a sequence of images 550-580are processed, and multiple appearances of an optical event, areidentified. In this particular example, sun glint 562 is determined tobe a suspected flash event. Following the suspected flash eventdetection phase, in which sun glint 562 is determined to be a suspectedflash event, an event of interest validation phase is implemented, andin this phase a motion tracking algorithm is applied to the multipleimages 550-580. The motion tracking algorithm attributes the sun glint562 reflected from the truck 552 and modulated by the intervening groveof trees 528, to motion of a single object intermittently obstructed bya chopper, and therefore using the event of interest criteria, thesystem concludes that the sun glint 562 is not a suspected flash event.

If at block 425 it is determined that the sample is not a suspectedflash event sample, the selection operation in block 430 is not invoked.It would be appreciated that according to examples of the presentlydisclosed subject matter, the detection (block 415), sample processing(block 420) and evaluation of the samples to determine whether they areindicative of a suspected flash event or not (block 425), as well as theimage capture (Mock 405) and memorizing (block 410) operations canresume uninterruptedly regardless of the results of the operations inblock 425.

According to examples of the presently disclosed subject matter,processing of suspected flash events and detection of events of interestinclude the various blocks and operations shown in FIG. 4 and describedherein, which can be invoked with respect to a plurality of opticalevents, in parallel (concurrent events), or in series, and/or whethersuch events are eventually determined to be event of interest or not.Still further by way of example, the limiting factors with respect tothe various blocks and operations shown in FIG. 4 and described hereinare related to the performance capabilities of the various components ofthe system which are used to implement and carry our the operations. Forexample, processing of the samples and/or of the images by theprocessor, reading of images from the frame buffer, etc.

Reference is now made to FIG. 6, which is a flowchart illustration ofthe method according to FIG. 4 in one possible implementation accordingto examples of the presently disclosed subject matter. Block 602represents the scene and the light (radiation) emitted, reflected,scattered etc., from the scene. In block 604 the radiation in the SWIRand visible bands is detected by a photodetector and sampled atapproximately 10 kHz (or at a slower rate if only flashes longer than 1ms are of interest). In parallel, an imaging unit, which operatesindependently from the photodetectors, captures SWIR images at 1000 FPS(or at a slower rate if only flashes longer than 1 ms are of interest)(block 606). By way of example, the images are stored in a FIFO memory(block 608).

At block 610 the samples from the photodetectors are processed using thesuspected flash event criterion, e.g., a prestored flash events library,other predefined criteria and/or heuristics. The comparison can becarried out continuously, e.g., for each new sample. It should be notedthat the process in block 610 can involve previous samples, and that oneor more previous samples can also be recorded in a buffer for thepurpose of carrying out the operation(s) in block 610. For example, todetect a signal rise which extends beyond a certain threshold, a fewsamples may be required. In another example, a few samples may berequired to rule out a possible transient which is not a reliable

At block 612 it is determined whether the samples from thephotodetectors are indicative of a suspected flash event this is theresult of the processing in block 610). Another operation which can beimplemented as part of the suspected flash event detection phase is todetermine whether two flashes (or more) that were detected by two (ormore) adjacent photodetectors at the same time relate to the same eventor represent two separate events. If it is determined that the samplesfrom the photodetectors are indicative of a suspected flash event, thesystem continues to operate (samples are obtained and processed andimages are captured and buffered) and no further action is necessary(block 614). As an option, one or more samples, and possibly imageswhich coincide in time with the samples, and possibly also other images(e.g. before or after the given samples) can be stored, e.g., forfurther investigation.

In case, however, it is determined at block 612 that the samples fromthe photodetector are indicative of a suspected flash event, atime-index is determined based on the timing of the samples from thephotodetectors, and images from the buffer are retrieved according tothe time-index (block 616). As mentioned above, the samples from thephotodetectors and the images from the imaging unit can be timecorrelated. The timing(s) of the samples which include radiationemission readings that correspond to a suspected flash event, whichprovide a temporal reference, is used for retrieving the images from thebuffer. As mentioned above, at least one of the images that is obtainedfrom the buffer can be an image of the scene before the start of thesuspected flash event or after the optical appearance of the suspectedflash event dissipated, or there can be at least one image which wascaptured before the start of the suspected flash event and at least oneother image that was captured after the optical appearance of thesuspected flash event dissipated (block 618).

Possibly in addition to the temporal relation among the photodetectorsamples and the imaging unit images, there may exist a spatial relation,when the photodetectors and/or the imaging unit have a multi-segmentedFOV. This may be the case when multiple photodetectors are used and/orwhen the imaging unit includes two or more cameras. In such cases, theFOV of each photodetector and each camera is spatially referenced so asto allow cross-correlation. By way of example, the cross correlation canbe used to select only images generated from a specific camera from thebuffer for a given time-index based on a spatial index, or to search foran optical signature of a suspected flash event within a certain regionof an image, etc.

According to examples of me presently disclosed subject matter, theimages that were retrieved front the buffer can be processed todetermine whether the suspected flash event is an event of interest ornot (block 620). As mentioned, the images can be processed using apredefined event of interest signature criterion.

Using the retrieved image and the time-index provided, based onprocessing of the photodetector samples, the optical signature of thesuspected flash event is detected in the images.

According to examples of the presently disclosed subject matter, in casean event of interest is detected, it can be communicated or otherwisereported (block 622). The communication or report can include variousdetails about the event of interest such as its location, aclassification of the event, etc.

Reference is now made to FIG. 7 which is a graphical illustration of anoperational time line for a detection method, according to examples ofthe presently disclosed subject matter. The time line 700 shows a firstband detection radiometry 702 and a second band detection radiometry 704over time. The photodetectors and the imaging unit operate continuouslyand independently regardless of whether an optical event (e.g., asuspected flash event) is taking place or not. For example, as can beseen in FIG. 7, as indicated by the samples stream 710 and by the framesstream 720, during the period between t0 and t1 ten samples are obtainedfrom the photodetectors, and a frame corresponding to camera exposure101 is captured, and during this period there are no significantradiation emission readings from the scene.

As indicated by the memory buffer block 730, the frames from the framesstream 720 are stored in the buffer. By way of example, the buffer canhold tens and even hundreds of frames. The buffer can be configured tokeep a certain number or up to a certain total capacity of frames, andcan use various buffer management algorithms to determine which frame todiscard to create space for incoming frames. For example, a FIFO buffermanagement scheme can be used. In another scheme, the buffer keeps acertain number of consecutive frames for a short time, but keepssparsely distributed frames for longer flashes or for tracking objectsover longer periods of time.

According to examples of the presently disclosed subject matter, at somepoint an optical event can occur. According to examples of the presentlydisclosed subject matter, samples from the photodetectors are fed to theprocessor. The samples which were taken when the optical event occurredcan be identified as being associated with a suspected flash event usingvarious processing methods. For example, U.S. Pat. No. 7,732,769 toSnider et al. discloses processing of samples of an optical event,

In U.S. Pat. No. 7,732,769 there is not a two-phase detection process asdescribed in the present disclosure. The final determination with regardto the optical event (i.e., whether it is an event of interest or not)is made, based on samples from the photodetectors. There are othersignificant differences between the examples disclosed herein and U.S.Pat. No. 7,732,769, however the processing methods which are applied tothe samples from the photodetectors can be used according to examples ofthe presently disclosed subject matter to determine whether an opticalevent is a suspected flash event. The processing of samples from thephotodetectors can also provide a time reference for extracting framesfrom the frame buffer. For example, the samples from the photodetectorscan give a temporal indication with regard to the occurrence of anoptical event, and this information can be translated to an index whichcan be used to extract relevant images from the frame buffer.

According to examples of the presently disclosed subject matter, thedetermination with regard to an optical event, as to whether it is asuspected flash event (or not) (also referred to herein as the suspectedflash event detection phase) can be based on samples which correspond toa majority of durations of the optical event. In a further example, thesuspected flash event detection phase can be based on samples whichcorrespond to the entire duration of the optical event, and in yetfurther examples, the suspected flash event detection phase can be basedon samples which correspond to a duration which is longer than theduration of the optical event. With respect to any one of theseexamples, and by way of further examples, the validation phase can becarried out after the suspected flash event detection phase iscompleted. A case where the suspected flash event detection phase isbased on samples which correspond to a duration which is longer than theduration of the optical event is depicted in FIG. 7, where the suspectedflash event detection phase extends to t30, by which time the opticalevent is over. This is in contrast to U.S. Pat. No. 7,732,769, where apreliminary detection decision is required (very quickly) based on theinitial rise of the flash. This translates into a significantly moredemanding link budget, processing power and latency requirement thanthose of the present invention. This is inherent to the concept oftriggering the imager, and is overcome in some examples of the presentlydisclosed subject matter at least by the use of continuous image captureto a buffer as described in the present invention.

When the processor determines that the optical event is a suspectedflash event, an index or any other appropriate reference is determinedfor images extracting from the buffer. For example, signal rise andsignal fall thresholds can be used to determine the rising and fallingedges of the signal from the photodetectors, and can be used todetermine the duration and the location on the time line of the opticalevent. It should be noted that according to examples of the presentlydisclosed subject matter, the signal rise and signal fall thresholds canbe identical or different and can be predefined or dynamically adjusted.

In FIG. 7, for example, the frame reference camera exposure 101-105 canbe retrieved. According to examples of the presently disclosed subjectmatter, using the references obtained through the processing of thephotodetector samples, at least a first image which includes readings ofradiation emission from the detected suspicious flash event, and atleast a second image which includes readings of radiation emission whichis not characteristic of the flash event are obtained.

According to examples of the presently disclosed subject matter, atleast one of the images obtained, based on the processing of thephotodetector samples (and the conclusion that a suspected flash eventoccurred), is an image which was captured prior to determination that asuspected flash event occurred. It would be appreciated that by using aframe buffer and an imaging unit that is configured to capture an imagecontinuously, it is possible to obtain one or more images of the scenewhere the optical event occurred, which precede identification of theoptical event as a suspected flash event, and even images which precedethe optical event.

As disclosed in the example provided above, at least one of the imageswhich are obtained (e.g., from the buffer) based on the processing ofthe photodetector samples can be an image which was captured prior tothe determination that a suspected flash event occurred. According toexamples of the presently disclosed subject matter, at least one of theimages obtained from the buffer, based on processing of thephotodetector samples, is an image which was captured prior to theoccurrence of the optical event (which was determined to be a suspectedflash event). In yet another example, at least one of the imagesobtained from the buffer based on the processing of the photodetectorsamples is an image which was captured after the optical event ended. Inyet further examples, the images which are obtained from the bufferbased on the processing of the photodetector samples include at leastone of: an image which was captured after the optical event ended, andan image which was captured before the start of the optical event.Processing of the images, including validation and geolocationfunctions, have been described above.

In FIG. 7, all the retrieved images, namely camera exposures 101-105,occurred prior to the determination that a suspected flash eventoccurred, and camera exposure 101 occurred before the optical eventwhich was determined to be a suspected flash event started.

According to examples of the presently disclosed subject matter, theretrieved images can be additionally processed to localize the flashevent. The geolocation function can involve determining by which imagepixel or by which group of adjacent pixels in an image that was capturedduring the occurrence of the suspected flash event, radiation from flashwas represented. Once the pixel or group of adjacent pixels whichrepresent the suspected flash event is identified, the hearing of theflash with respect to the system orientation is determined. In someexamples the order in which the geolocation function and the validationfunction can be implemented is in any order with respect to one another.In another example, the validation function can be concluded after thegeolocation function is carried out. If the latter configuration isused, the results of the geolocation function can be used by thevalidation function. Thus, for example, once one or more pixels (or oneor more adjacent pixel groups) are geo-located, the validation functioncan be used to determine which, if any, of the geo-located pixels (or ofthe groups of adjacent pixels) is a valid event of interest. Forexample, as part of implementation of the geolocation function, a motionvector assisted image subtraction operation can be applied. The imagesubtraction operation can involve subtracting from an image or images inwhich the suspected flash event appears, an image in which the suspectflash event does not appear (e.g., an image taken before or after thesuspected flash event). The motion vector can be used to account for anoffset (e.g., a two dimensional offset) among different images, thuscontributing to reduction of the residual clutter in the differenceimage.

Once the bearing of the suspected flash event (or if it was validated:the bearing of the event of interest) with respect to the system isknown, it can be translated to a absolute bearing in geographic space byusing additional data, such as location data from a GPS unit and/or aIMU unit for example. An example of a flash location function that isimplemented as part of a flash detection process and using a flashdetection system is disclosed for example in U.S. Pat. No. 7,732,769.Techniques to enhance the location performance were discussed above,including the use of motion vectors for background subtraction, timedependent signal extraction from the imager and comparison with thetime-dependent signals from the photodetectors, etc.

Still further according to examples of the presently disclosed subjectmatter, a classification function can be implemented as part of theflash detection process to provide estimation with respect to the typeof flash or with respect to the source which generated the flash. Theclassification of the suspected flash event or of the event of interestcan be based on known flash characteristics of various flash typesand/or of various flash sources, such as temporal signatures and/orspectral signatures. One example of a classification function isdisclosed in U.S. Pat. No. 8,421,015 to Scott et al., using waveletsanalysis and other techniques.

According to examples of the presently disclosed subject matter, theidentification of an event of interest and possibly also finding thelocation (e.g., bearing, and in some cases range) of the event ofinterest, and possibly also the classification of the event can becommunicated to various destination points, such as a firing system, anintelligence database, a control and command center, etc.

Reference is now made to FIG. 8, which is a simplified block diagram ofa photodetectors array and a camera array which can be used in adetection system according to examples of the presently disclosedsubject matter. According to examples of the presently disclosed subjectmatter, the detection system 800 has twelve photodetector sector units810A-810L each capable of monitoring a 30° wide horizontal sector andmonitoring the sector for visible light and SWIR or MWIR radiation.Collectively, the photodetector section units 810A-810L provide a 360°horizontal coverage.

According to examples of the presently disclosed subject matter, thedetection system 800 has an imaging unit 820 that consists of six SWIRcameras 822A-822F, each covering a horizontal FOV of 60° and togetherproviding a 360° horizontal coverage.

In the detection system 800 which is partially depicted by way ofexample in FIG. 8, each camera has a FOV that is covered by twophotodetector sector units. Thus, according to examples of the presentlydisclosed subject matter, when an optical event is picked up by one ofthe photodetector sector units, and it is determined that the opticalevent is a suspected flash event, the detection system 800 (e.g., theprocessor) retrieves from the buffer images that were captured by thecamera whose FOV covers the FOV of the photodetector sector unit thatdetected the suspected flash event. This can be achieved by mapping thephotodetector sector units and the cameras which have overlapping FOVs,and marking or indexing the photodetector samples and the images storedin the buffer.

In further examples of the presently disclosed subject matter, sinceeach photodetector sector unit covers only a portion of the FOV of eachcamera, the images retrieved from the buffer can be cropped so that itis only necessary to process the portion of the image that correspondsto the FOV of the photodetector sector unit which detected the suspectedflash event which led to the retrieval of the images from the buffer. Inorder to enable cropping of the images, the mapping of the photodetectorsector units and the cameras which was mentioned above can also includean indication as to which portion of the camera's FOV is covered by theFOV of which photodetector sector unit, and thus when detection of asuspected flash event is made, based on samples from a certainphotodetector sector unit, the detection system can determine whatportion of the retrieved images needs to be processed in order to thedetermine whether the suspected flash event is an event of interest ornot.

It would be appreciated that the number of cameras and photodetectorsector units, the relation between the cameras and photodetector sectorwilts and their FOV in FIG. 8 is merely one of many possibly examples,and that other numbers and relations are contemplated according toexamples of the presently disclosed subject matter.

Reference is now made to FIG. 9, which is a block diagram illustrationof a simplified block diagram of a photodetector array, a camera array,and a FOV controller, which can be used in a detection system accordingto examples of the presently disclosed subject matter. In FIG. 9, theconfiguration of the photodetector sector units 910A-910L, to theconfiguration of the photodetector sector units 810A-810L in FIG. 8,with each photodetector sector unit capable of monitoring a 30° widehorizontal sector, monitor the sector for visible light and SWIR or MWIRradiation. Collectively, the photodetector section units 910A-910Lprovide a 360° horizontal coverage.

What is different is the configuration of the imaging unit 920. Theimaging unit 920 in FIG. 9 includes only 2 SWIR cameras 922A and 922B.In the optical path of each one of the SWIR cameras 922A and 922B thereis a FOV combiner 924A and 924B, respectively, that superimposes threedifferent FOVs 926A-926C and 926D-926F to form a combined FOV. Each oneof the FOV combiners 924A and 924B feeds the combined FOV to a SWIRcamera 922A and 922B, respectively. The SWIR camera 922A and 922Bgenerates an image which is constructed of three superimposed FOVs926A-926C and 926D-926F, respectively. Similar FOV combiners arepresented and discussed in detail in WO2008129552. By way of example, itmay be assumed that a flash occurred within the FOV of photodetector910E. The same flash was captured by SWIR Camera 922B. The geolocationfunction can find the pixel SWIR Camera 922B where the suspected flashradiation was captured. However, due to the combining function of FOVcombiner 924B, there is an ambiguity in the SWIR camera 922B regardingthe FOV where the flash radiation was obtained. The rough geolocationprovided by the photodetector (in this case 910E) resolves thisambiguity—it is clear that the flash must have been recorded by FOV 926Eand not by FOV 926D nor by FOV 926F because photodetector 910E overlapsFOV 926E alone.

There is provided according to a further aspect of the presentlydisclosed subject matter a system for providing a geolocation of asuspected flash event. According to examples of the presently disclosedsubject matter, the system can include a frame buffer, one or morephotodetectors, and a controller. The frame buffer can be capable ofmemorizing a sequence of high-resolution images of a scene. The one ormore photodetectors can be capable of obtaining radiation emissionreadings from the scene. The controller can be configured to detect asuspected flash event based on processing the radiation emissionreadings from the one or more photo detectors, where the detection ofthe suspected flash event occurs at a first instant. The controller canbe further configured to retrieve from the buffer high-resolution imagesof the scene including at least one image that was captured prior to thefirst instant, and is further configured to process the high-resolutionimages of the scene to determine a geolocation of the suspected flashevent.

Still in accordance with a farther aspect of the presently disclosedsubject matter, there is provided a method of determining a geolocationof a suspected flash event. According to examples of the presentlydisclosed subject matter, the method can include: memorizing a sequenceof high-resolution images of a scene in a buffer; obtaining radiationemission readings from one or more photo detectors; detecting asuspected flash event based on processing the radiation emissionreadings from the one or more photo detectors, wherein said detectingoccurs at a first instant; and retrieving from the bufferhigh-resolution images of the scene including at least one image thatwas captured prior to said first instant; and processing thehigh-resolution images of the scene to determine a geolocation of thesuspected flash event.

It should be noted that the system for providing a geolocation of asuspected flash event and the method of determining a geolocation of asuspected flash event can be implemented based on the teaching providedabove with or without the operations and configurations which wereimplemented to determine whether a suspected flash event is an event ofinterest or not.

Instead of the operations and configurations which were implemented todetermine whether a suspected flash event is an event of interest ornot, the system for providing a geolocation of a suspected flash eventand the method of determining a geolocation of a suspected flash eventinclude operations for determining a geolocation of an optical eventthat was determined to be a suspected flash event based on theprocessing of the radiation emission readings from the one or more photodetectors.

The configuration of the controller and the processing of the radiationemission readings from the one or more photo detectors to determinewhether the reading corresponds to a suspected flash event was describedin detail above, and the teachings provided above are also applicable tothe system for providing a geolocation of a suspected flash event andthe method of determining a geolocation of a suspected flash event whichare now discussed.

The configuration of the controller and the processing of thehigh-resolution images, possibly in combination with the radiationemission reading prom the one or more photodetectors, to determine ageolocation of an optical event was described in detail above. It isnoted that in the description provided above, the optical event was asuspected flash event that was determined to be an event of interest,and in the present aspects, namely in the system for providing ageolocation of a suspected flash event and in the method of determininga geolocation of a suspected flash event, the geolocation processingdoes not necessarily follow a validation of the suspected flash event asan event of interest, and can be applied without such validation (i.e.,when an event is determined to be a suspected flash event, but is notnecessarily a validated event of interest).

Reference is now made to FIG. 10 which is a block diagram illustrationof one possible implementation of the system in FIG. 1, according toexamples of the presently disclosed subject matter. The system in FIG.10 (referenced 1000) is similar in structure and operation to the systemshown in FIG. 3, and the features which share the same numeral ascorresponding to features in FIG. 3 have similar structure and areconfigured in a similar manner. Accordingly, the relevant parts of thedescription of such features is applicable mutatis mutandis to thedescription of the corresponding features in FIG. 10. Notwithstandingthe above, it should be noted, that while the capabilities andconfigurations of features in FIG. 10 and their counterparts in FIG. 3can be similar or events may be identical, it can also be differentwithin the range of possibilities set forth in the description of suchfeatures provided above. For example, the suspected flash eventcriterion that is used by the controller component 372 is notnecessarily identical when it is used in the context of the system shownin FIG. 3 compared to the definition of the same criterion when used inthe context of the system shown in FIG. 10. Thus for example, in thecase of the system shown in FIG. 10, the criterion can includeparameters which put stronger emphasis on certain characteristics of theoptical event under evaluation, whereas other characteristics are moresalient in the criterion that is employed by the system shown in FIG. 3.

In a similar manner, the geolocation module 1076 in FIG. 10 implements ageolocation function or procedure, such as described above, for example,with reference to FIG. 3, but according to the present aspect of thepresently disclosed subject matter system the geolocation module 1076and the geolocation process implemented by the geolocation module 1076do not necessarily involve or require that the detected suspected flashevent is validated as an event of interest. In this aspect, for example,it can be assumed that the suspected flash event is an event ofinterest. Further by way of example, a validation phase such as the onedescribed above, in which a detected suspected flash event is evaluatedto determine whether it is an event of interest or not can beimplemented by the controller 1070.

As is shown in FIG. 10, block 1076 which is a component or a module ofthe controller 1070 is configured to implement the geolocation functionor process, and the validation phase is not required.

Reference is now made to FIG. 11, which is a flowchart illustration of amethod of determining a geolocation of an optical event according toexamples of the presently disclosed subject matter. The methodillustrated in FIG. 11 includes operations which are similar to thoseillustrated in FIG. 6, and which were described above with reference toFIG. 6. The operations in FIG. 11 which share the same numeral ascorresponding operations in FIG. 6 are similar and the relevantdescription which was provided above in particular with reference to thecorresponding operations is applicable mutatis mutandis to theoperations of the method shown in FIG. 11. Notwithstanding the above, itshould be noted, that some difference can exist within the range ofpossibilities set forth in the description of the correspondingoperations provided above. In addition, as can be seen in FIG. 11, themethod of determining a geolocation of a suspected flash event includes,at block 1120, determining a geolocation of a suspected flash event. Thegeolocation determination operation does not require a validation phase,whereby a suspected flash event is evaluated using hi resolution imagesobtained from an image buffer to determine whether the suspected flashevent is an event of interest or not (block 620 in FIG. 6), although insome examples, such an operation can also be implemented as part of themethod of determining a geolocation of an optical event.

It will also be understood that the systems described herein may be asuitably programmed computer. Likewise, the invention contemplates acomputer program being readable by a computer for executing the methodof the invention. The invention further contemplates a machine-readablememory tangibly embodying a program of instructions executable by themachine for executing the method of the invention.

The invention claimed is:
 1. A method comprising: obtaining, from adetection system including at least one imaging unit and one or morephoto detectors, a sequence of high-resolution images of a scenecaptured by said at least one imaging unit of the detection system, andradiation emission readings measured from the scene, by said one or morephoto detectors of the detection system; processing the radiationemission readings obtained from the one or more photo detectors todetect a suspected flash event; processing the high-resolution images todetermine a location of the suspected flash event; and processing saidhigh-resolution images to determine whether the suspected flash eventoccurred or not, wherein the determining of whether the suspected flashevent occurred or not comprises applying motion processing to thehigh-resolution images to identify a moving object in the scene; anddetermining whether the suspected flash event is associated with glintfrom said moving object, by processing the high-resolution images todetermine whether said location of the suspected flash is associatedwith said moving object; thereby enabling to validate or disqualifyoccurrence of the suspected flash event.
 2. The method of claim 1,wherein the determining of whether the suspected flash event occurredcomprises determining whether the suspected flash event is associatedwith the glint from said moving object while said moving object ismoving in the scene behind a chopping object.
 3. The method of claim 2,further comprising disqualifying occurrence of the suspected flash eventupon determining that the suspected flash event is associated with saidglint from the movement of said moving object behind the choppingobject.
 4. The method of claim 2, wherein the chopping object is atleast one of a grove of trees and a fence.
 5. The method of claim 1,wherein the determining of the location of the suspected flash eventcomprises retrieving, from the sequence of high-resolution images, atleast one image without the suspected flash event and at least one imagewith the suspected flash event, and subtracting the at least one imagewithout the suspected flash event from the at least one image with thesuspected flash event to locate the suspected flash event within theimages.
 6. The method of claim 5, wherein said subtracting is performedby utilizing a block-by-block motion correction to thereby accuratelyremove background from the image with the suspected flash event.
 7. Themethod according to claim 5, wherein said retrieving comprisesdetermining said at least one image without the suspected flash eventand said at least one image with the suspected flash event, bycross-correlating samples of the radiation emission readings from theone or more photo detectors and timings of said high resolution images.8. The method according to claim 1, further comprising continuouslyoperating a high-resolution camera to capture the high-resolution imagesof the scene independently from the photodetectors, and regardless ofdetection of the suspected flash event.
 9. A method comprising:obtaining from a detection system including at least one imaging unitand one or more photo detectors, a sequence of high-resolution images ofa scene captured by said at least one imaging unit of the detectionsystem, and radiation emission readings measured from the scene, by saidone or more photo detectors of the detection system; processing theradiation emission readings from the one or more photo detectors todetect a suspected flash event; and processing the high-resolutionimages captured by the at least one imaging unit, to determine alocation of the suspected flash event, wherein the determining of thelocation of the suspected flash event comprises: retrieving, from thesequence of high-resolution images, at least one image without thesuspected flash event and at least one image with the suspected flashevent, the retrieving comprising determining said at least one imagewithout the suspected flash event and said at least one image with thesuspected flash event, by cross-correlating samples of the radiationemission readings from the one or more photo detectors and timings ofsaid high resolution images; subtracting the at least one image withoutthe suspected flash event from the at least one image with the suspectedflash event to locate the suspected flash event within the image; andprocessing the high-resolution images to determine whether the suspectedflash event occurred or not, by applying motion processing to thehigh-resolution images to identify a moving object in the scene anddetermining whether the suspected flash event is associated with glintfrom said moving object.
 10. The method according to claim 9, whereinsaid subtracting is performed by utilizing a block-by-block motioncorrection to remove background from the image with the suspected flashevent.
 11. A system comprising: a detection system including: at leastone imaging unit capable of capturing a sequence of high-resolutionimages of a scene sequence, and one or more photo detectors capable ofobtaining radiation emission readings from the scene; a frame bufferconnectable to the at least one imaging unit of the detection system andcapable of memorizing the sequence of high-resolution images of thescene, which are captured by said at least one imaging unit; acontroller connectable to the one or more photodetectors of thedetection system, which provide radiation emission readings from thescene, and configured and operable for detecting a suspected flash eventbased on processing the radiation emission readings from the one or morephoto detectors; and wherein the controller is configured fordetermining whether the suspected flash event occurred or not, byprocessing the high-resolution images captured by said at least oneimaging unit, whereby said processing of the high-resolution imagescomprises: applying motion processing to the high-resolution images ofthe scene to identify a moving object in the scene; processing thehigh-resolution images to determine a location of the suspected flashevent; and determining whether the suspected flash event is associatedwith glint from said moving object by determining whether said locationof the suspected flash is associated with said moving object; therebyenabling to validate or disqualify occurrence of the suspected flashevent.
 12. The system of claim 11, wherein in determining whether thesuspected flash event occurred or not, the controller further determineswhether the suspected flash event is associated with said glint from themoving object while the moving object is moving in the scene behind achopping object.
 13. The system of claim 12, wherein the controller isadapted to disqualify occurrence of the suspected flash event, upondetermining that the glint associated with the movement of the movingobject is behind said chopping object.
 14. The system of claim 11,wherein the controller is adapted for carrying out the following fordetermining said location of the suspected flash event: retrieving, fromthe sequence of high-resolution images, at least one image without thesuspected flash event and at least one image with the suspected flashevent; and subtracting the at least one image without the suspectedflash event from the at least one image with the suspected flash eventto locate the suspected flash event within the images.
 15. The system ofclaim 14, wherein the controller is configured for carrying out saidsubtracting by utilizing a block-by-block motion correction to therebyaccurately remove background from the image with the suspected flashevent.
 16. The system of claim 14, wherein said retrieving comprisescross-correlating samples of the radiation emission readings from theone or more photo detectors and timings of said high resolution imagesto determine said at least one image without the suspected flash event,and said at least one image with the suspected flash event.
 17. Thesystem according to claim 11, wherein the controller is connectable to ahigh-resolution camera that operates continuously to capture thehigh-resolution images of the scene independently from thephotodetectors and regardless of detection of the suspected flash event.18. A system connectable to a detection system including at least oneimaging unit, and one or more photo detectors, for detecting flashevents; the system comprising: a frame buffer connectable to the atleast one imaging unit of the detection system and capable of memorizinga sequence of high-resolution images of a scene captured by said atleast one imaging unit; a controller connectable to the one or morephotodetectors of the detection system for obtaining, from said one ormore photodetectors, radiation emission readings from the scene; saidcontroller is configured and operable for detecting a suspected flashevent based on processing the radiation emission readings from the oneor more photo detectors, and determining whether the suspected flashevent occurred or not, by carrying out the following processing on theradiation emission readings from said one or more photo detectors andsaid high-resolution images captured by said at least one imaging unit:applying motion processing to the high-resolution images of the scene toidentify a moving object in the scene; processing the high-resolutionimages to determine a location of the suspected flash event by: (i)cross-correlating samples of the radiation emission readings from theone or more photo detectors and timings of the high resolution images ofsaid sequence to determine at least one image without the suspectedflash event, and at least one image with the suspected flash event; (ii)retrieving said at least one image without the suspected flash event andsaid at least one image with the suspected flash event from saidsequence of high resolution images; and (iii) subtracting the at leastone image without the suspected flash event from the at least one imagewith the suspected flash event to locate the suspected flash eventwithin the images; and thereby determining whether the suspected flashevent is associated with glint from said moving object.